Turan is a major power of the Hyborian world, it's quite a shame we don't have a sourcebook yet (hear this Mongoose people). It would perfectly complete the Zamboula sourcebook everyone is waiting so eagerly.
In the meantime, you can always try this:
There's a description of Aghrapur in Signs & Portents 32, downloadable for free on Mongoose site.
You'll find also some nice info on Thulsa's site hyboria.xoth and on the dark storm legends site.
You might also take a look at this old Conan/AD&D module, CB1 Conan unchained. It contains information on the Kozaki and the Red Brotherhood of the Vilayet. Both are rebelious factions that play an important role in Turan.
With a bit of reworking, you'll find the adventure very "conanesque".
Take also a look at my thread on this forum "help needed-hyborian timeline" for info on the Turanian Kings.
My own campaign is centered around Turan and the Eastern Desert, so I'll be happy to share any information.
And of course, don't forget "Devil In Iron" and "Iron Shadows in the Moon" from REH. They're worth any sourcebook you could get...