We do not have math circles in our area and I unfortunately don't have the time to start one
There are several Math Circle books available on Amazon. Those are an excellent resource for him to work on math, critical thinking, logic and reasoning (if you cannot find them, let me know and I will add the link to the books).
Also, there are books for Math Kangaroo preparation by Borac (again amazon).
If you go to the math kangaroo US website, they sell all the old MK question papers for reasonable prices. I bought the whole lot for my DS to work on for fun (the answer keys are in their website and you don't have to buy them).
MK Canada has all the old question papers for free here:
https://kangaroo.math.ca/index.php?kn_mod=samplesI would also recommend MEP math. it is free and you can print out the pages that you think might interest your DS. They have a lot of "puzzle" type math problems.
http://www.cimt.plymouth.ac.uk/projects/mepres/primary/Good luck.
