If you are looking for a general area with active troll roleplayers of ‘this tribe’, I’m afraid I don’t know since most troll roleplayers bunch up together no matter what tribe they are and either way, it’s guild orientated.
The Darkspear Warband is souly a Darkspear guild, Painted Shields is based on the rastari from Zandalar but has also recruited trolls from other tribes besides the Zandalari and the Hand of Zul have a lot of tribes in it.
However, there is also an active discord for the troll RP community so if you wish to get in touch with the troll RPers and these guilds I mentioned, I suggest you start your search there.