J. Kihope shows the 3D-Printed FPG9 Kit For 3rd Gen G17s/18s GBB Pistols from Tokyo Marui and WE Airsoft. Further mods are required in order to fit the kit properly...
J. Kihope does an assembly of the IAP 3D-Printed AK-200 Conversion Kit that will turn a compatible AK-47 to look like an AK-200, which is the earlier version of what became to be the AK-12 rifle. If you want to do it, you can purchase and download the 3D files that you can use, provided that you have access to a 3D printer.