I have purchased several Real Steal Blackhawk holster from here without issue (including my Glock 21 holster to support my TM G17/18c)
You can also get the necessary S.T.R.I.K.E plate to place on your carrier:
https://encrypted-tbn2.gstatic.com/i...eMWnwf5spjRFob
Lead times vary from 1 week to 1 month depending on availability.
Call them:
http://www.rnicholls.com/en/contact.php