Finally picked up a GG&G adapter for my USP9SD : r/HecklerKoch
HK Picatinny Rail Flashlight Mounts| HK USP Flashlight Mounts | GG&G Tactical Accessories
H&K USP Compact Tactical - An HK USP 45 CT with barrel thread protecter, GG&G rail adapter with a 2nd Generation Viridian X5L green laser sight and tactical light. | Facebook
GGG Pistol Flashlight Adapter - USP Full Size - HKPARTS