An IDPA holster must be strong side straight draw belt, paddle or IWB type. No drop or offset (except for a woman.) No clamps, clips, rails, pegs, or magnets, the gun must go IN the holster, with coverage at least to within 1/4inch of the front of the ejection port.
You could take any IDPA holster to a USPSA shoot but not vice versa.
I use RTP, seen at
www.pistolpacking.com
but there are others in kydex and leather.