I recently discovered an electric (rechargeable) semi and full auto airsoft Glock 18 and tried my best to find one to buy. The problem is, they were Chinese made copies that were never authorized by Glock and have since been discontinued so, all the ones currently in the U.S. are all that will ever be.
After weeks of searching, I kept coming up empty. Websites would show to have them in stock until I tried to actually buy one, which is when it would show up as "out of stock".
I finally ended up finding one that looks like a Sig Saur but, all the other specs are identical to the Glock version. Same rate of fire, FPS, battery type, 30rnd mag, etc. It's quite accurate up to about 70ft. After that the BB's tend to curve to the right. On full auto, it shoots insanely fast at just under 900 rpm which means you can empty the entire magazine in about 3 seconds.
I have 2 CO2 pistols as well. One is modeled after a Beretta 92, is non-blowback and shoots at about 450 fps. The other is modeled after a Walther P99, is officially licensed and therefore has all the same markings as the real thing, has blowback (which causes an annoyingly loud "clink" from the metal slide each time it is fired) and shoots at about 410 fps.
I've tried to stay away from green gas guns as much as possible. The gas isn't locally available and the nearest place that sells airsoft supplies is 60 miles away. I know you can use propane if you add silicone every so often but, that smells really bad. I heard somewhere that there was a CO2 conversion kit available but, a friend blew the seals out of one of his 40mm grenades and 2 pistol mags trying that.