I have a blackhawk serpa thigh holster I had got for a Glock 17, all I did was take a serpa holster for my xd, swap it out, and presto, thigh holster for the xd
Safariland part# 6004-149-121 (RH) is a tactical drop leg thigh rig made for duty use. It isn't cheap, but it is quality stuff. It is available at any LE supply store that sells Safariland products.