Titanium Tactical Industry Folding Thumb Rest for Action Army AAP-01 Gas Blowback Airsoft Pistols
(Color: Red / Left Side)

"Just got mine yesterday. Installed in five minutes, and it works well. The four stars are because the lower pin that holds the rest is just the one from the pistol frame, but pushed a little further in. This causes two problems, the first is that I feel like the pin is less effective at holding the trigger group in if it's not completely seated, and the second is that the thumb rest isn't completely immobile, and will rotate with enough pressure. Normal target shooting shouldn't be a problem, but when moving and shooting, or climbing around a field, I could easily see the rest rotating. I plan on drilling the thumb rest out and fabbing up a screw to go through the frame, so it will be mounted solidly.

If you're looking for install videos, there aren't any, but other brands' videos did the trick for me.