A couple of guys on hkpro decided to do their own mk23 pic rail adapter, and it turned out great! : r/HecklerKoch
STL file MK23 TO M4 HPA ADAPTER・3D printer model to download・Cults
GG&G Picatinny Rail Adapter HK MK 23 Aluminum Matte
Nineball 14mm NEO SAS Silencer Attachment System for Tokyo Marui SOCOM Mk23 Gas Airsoft Pistol, Accessories & Parts, Gas Gun Parts, Barrel Adapters - Evike.com Airsoft Superstore