There is no such central directory or community. RPGs are largely edited by people who have connections with the designer(s). Whether it's a big game publisher with professional connections to editors and editing agencies, or it's an independent designer who knows a semi-pro game editor on Twitter, the pattern is the same: who you know is how you connect with the people with the talents and skills you're looking for.
Start by considering your social and professional networks. Put out the word that you're looking for an editor. With a Kickstarter behind you, that's a resource you can lean on too – use the buzz around that, and the communications channels you've established during the campaign, to put out word that you want to bring on someone from outside for additional editing.
I know of a bunch of people who do game editing professionally, but who I know of doesn't help you, because they're not your connections, and I don't have a strong enough connection to pull on it and connect them to a stranger. Game editors are out there though – go meet them.