For those who are looking for spare parts and accessories for their CYMA AEGs, 18Airsoft posted some available at their website. You can check the gearboxes they have for the AK series and the USP AEP, scope mount for the SVD, M24 Aluminium Cylinder Set, and the CYMA P90 Outer Barrel. Click on the links below to learn more:

CYMA Aluminum SVD Scope Mount

CYMA Aluminum Cylinder Set for CYMA M24/CM705

CYMA Outer Barrel for CYMA P90

CYMA High Torque Gearbox Set for CM-028 AK Series

CYMA Gearbox for CM125