there are a bunch of custom maps but they don't seem to be popular with that many players, probably due to a number of reasons (it is a pain to install them, p2p downloading wasn't always working, there is a 50 map limit, some maps have multiple versions, not all of them are suited for competitive play, some graphical issues, some guns not working, some maps not working)
for coop you can join the discord and a text file will inform you with the current state of co-op. it is absolutely not perfect but it can work in some cases.
this is the link of its current state
https://pastebin.com/Ep3QMULs