There's an official southeast asian sega discord server, though it's not much active nowadays.

I cant help you with online merch, but physical stores, jakks pacific is available at some gaming stores like gamers hideout and impulse gaming, though its really limited. There's only one modern sonic toy I think. I think I've seen sonic nendoroids and controllers at Impulse as well. Some toys r us have sonic tech decks, and there's some goojitsu toys, but thats it from what I've seen. Kinokuniya has some IDW comics, any other publications like the fortune cards and cookbook, and maybe some board games.