I honestly don't know many 'communities' but Vintage Synth [1] is great. It's hard to avoid Gearslutz, you'll see it googling. Hydrogen Audio [2] is one of the better music communities I know, apart from Jemsite, but it's mostly digital/software/algorithm stuff. Maybe Future Producers [3] is more your thing. Or check synth-specific forums (I don't know what you've got). [4,5]