For a more serious reply: As already stated CORPS is good in this regard, but are also playing strategic games.
Now for my suggestions in order(1 is the best to join and so on).
(as a semi role-player myself i gotta suggest this clan they are a great bunch of people, there as some good ones stopped playing recently but the one renaming should still be fire and ready for some new blood--> ived played a lot with guys from this clan)(ps. this clan is always looking for members to add to their regular role-play diplo games).
3.The Roleplayers Guild https://www.warzone.com/Clans/?ID=3
(i only belive they are roleplaying, but havent played that much with em, i belive they have more clan only role-play games).
4.Nuke Diplomacy https://www.warzone.com/Clans/?ID=372
(they are currently playing in CL meaning strategic leuge basicly, but i belive they are role-players too. They have had some bootes lately, but they are few, so might be worth a shot).
5. Roleplayers Realm https://www.warzone.com/Clans/?ID=68
(there are pretty many of them, unknown who many actually plays i dont know rly).
6.The Last Alliance https://www.warzone.com/Clans/?ID=349
(this is a newer role-play clan maybe they are more active, than no.5? whos from 2013?).
Well there you got it, they ones i know have been known by most, but again no.1, 2, 3 are the best options really. Good luck, hunting role-players!