I'm kinda on the hunt for one of these myself. The USPc in 45 does not get much holster love, unfortunately. In another thread I posted recently in this forum, I mentioned that I was surprised to find the JM Custom and several other top-tier makers don't mess with this model at all.
Right now, a couple days into research, I'm leaning towards G-Code's options. They make top quality kit at startlingly reasonable prices. I have had several of their products starting about ten years ago, and regularly run my 'OSH' holster for my P2000; they make it for the USPc45, and the bottom is open to accommodate the threaded barrel. I would actually prefer the 'XST' holster for my application (this kit would be for direct action tasks), but you have to use their 'RTI' system for the XST, which nearly doubles the costs to get it on your hip after you buy the mounting accessories. The RTI system is quite nice, however, if you are switching your handgun from your hip to a chest rig, plate carrier and a vehicle mounted RTI clip--but is a bit overkill if that's not your lifestyle. The OSH has great adjustable tentsion, and I wouldn't worry about it coming loose in non-extreme circumstances.
I hope this helps, and good luck on the search. Please report back when you buy!