I've created 8 custom coop maps, some of them are a bit hard, and was wondering ... if they aren't modded like some of the maps here, where do I go to promote them?

Thanks. Crazy

In the case they aren't made in the Hammer editor but by using the PTI puzzle maker, make sure to upload them at the Portal2's "Released Maps - PTI" section. If they're Hammer maps, just use the "Released Maps - Coop" section.