Hi,
Just letting you know that you are correct about Criimson Trace & Lasermax- they don't make products for H&K USP .40 Fullsize. You can get a Streamlight TLR-2 which is a light/laser combo.
I can provide the
Streamlight TLR-2, the H&K Rail adapter, and the TLR-2 Carrier for
$294 including shipping.
You'll need the TLR-HK Adapter to fit on your H&K Rail.
As far as the holster goes- umm lol unless its for duty- you're kinda out of luck.
Conversely you could carry the tac light/laser with something like this:
Link Removed
Other than the above options I don't see a way...
sorry