That is a SUPER tough question. For some people making friends is easy, for others it is something that takes conscious effort and does not come easily.
For starters it would be important to make sure he knows that its not QUANTITY that matters but quality. One good friend is worth so much more than 10 acquaintances. The other thing he needs to know is that not EVERYONE will have a "best friend" through all of life. Some people will tend to flit from group to group, having fun with each but not staying too long. I think in school-aged children there is a lot of focus on "BFFs" (although perhaps that is more of a girl thing?) so kids without a "best friend" tend to feel as if they are missing something or otherwise haven't succeeded at friend-making. While quality is great, there will be stages of life where one simply does not have a "best friend" and there is nothing wrong with that either. It doesn't mean there is anything wrong with HIM.
("What is wrong with me, why can't I make friends?" Answer: "Nothing. He just has different interests and prefers different things and there is nothing wrong with that.")
Speaking personally:
I fall into the "making friends is HARD" category. In elementary school I had ONE good friend. Highschool I had a handful of friends but we weren't the sort that made much effort to hang out outside of school. It wasn't until university that I met someone like-minded enough that I would consider them a "best friend". Then they moved away and again I was "friends" with most classmates but never "best friends" with anyone. Now in adult life I have my friend circle and it totally revolves around shared interests. I still find it VERY hard to be friends with people with whom I share no common interests with.
I'm not going to lie: It has been lonely. I've certainly gone through the "why don't I have any friends" stages and those sucked, but you and he should know that it gets better. As he grows he will find his niche and his people.
Speaking less personally:
the vast majority of the other boys are... not who he'd be friends
with
It might be a bit "taboo" at that age, but girls are a friend-option too! :)
He's fairly quiet/shy, loves football (soccer) and chess and reading
and crafts.
Are there clubs for any of these things at his school? Are there teachers who would be willing to supervise or run a club for any of these things? If so, if he can get involved with a group (or help START a group) to do these things then it would help him get more connected with the kids at school. Even if they aren't in his class, they are in the same school, maybe the same grade and that means they can meet at lunch and whatnot. If there are no teachers who would/would supervise/run a club then perhaps he could take a soccerball or a small chess-set to play with at lunchtime and find his own people. Unfortunately the "quiet/shy" will make this a bit more of a challenge as he is unlikely to want to shout for a chess-partner from the top of the playground. Again, perhaps a teacher could help him find others who would be happy to play chess at lunch. There are many other board games too, perhaps he would have more luck finding game-players with some other games.
For "outside of school" friends, the local community center may have some sort of club or class that fits his interests. You mentioned he likes crafts, there are often craft-related classes put on at local community centers or libraries in my area. It would be worth a look - prioritize ones that require teamwork or interaction with others. I know you didn't ask about helping him overcome his shyness but it occurred to me that a drama/acting/improv class might be something he would enjoy that would also help him a little with shyness. (My husband is an introvert and there is NOTHING wrong with not liking "undefined social situations", but it does make making new friends a bit hard.)
Even a homework-club could be something that would give him opportunities to get to know other kids his age.
Also, consider that for non-physical activities he may connect better with kids slightly older than him (I did when I was a kid) so don't be afraid to test out things where he is with older kids. It might work out. Although you said he was one of the younger kids in his class, so maybe testing an activity out where he is one of the somewhat older kids may work.
As far a supporting him with this beyond just setting up opportunities to meet potential friends: make sure you get the contact info of the parents of any kids he seems to be "clicking" with at any of these activities.
What I want to do is give him a really good answer about how to make friends. With some concrete suggestions.
I think this is the hardest part to answer. There is no "easy way" or "one-size-fits-all" solution. Making friends can be HARD. Not everyone will want to be your friend, you won't want to be everyone's friend. Best "general answer": Be kind, show interest, listen, and do your best to ask questions to draw out more about their interests. The most important thing though is to not try to "put on an act" to be someone who he may think others want him to be. If he is a bit introverted by nature then he will develop an "outgoing persona" ("Quiet" by Susan Cain is an interesting read if you think he may be somewhat on the introverted side of things), but he shouldn't make up a whole new personality or force or fake an interest in something he hates. (Thats not to say he can't learn to show interest in other people's hobbies though. Just that there is a big difference between "I heard your favourite sports team won! You must be stoked!" and "oh yes, I also love sports-team-I-know-nothing-about!")
My own personal strategy is to be super blunt with "Hi, I'm ___. Nice to meet you! So what are you into? What are your hobbies? Hows life?"
This rambled a bit but I hope there is something here that can help. Making friends is hard. Having a hard time making friends is hard. Its not easy or fun knowing that everyone else has a "best friend" while you struggle to find someone to hang out/play with for a few hours or at lunch. Not having that "instant partner" for class projects sucks. But it will get better. Eventually.
