Seriously guys I own a lot of airsoft guns, both springers and AEGs. I think everyone is going to find that for the pistols there just isn't going to be enough room inside them, especially the springers. Even after you take out the metal inner barrel there is no way you can mount the sensor and board in there. It's possible for some of the bigger handguns that you probably could remove the sensor and mount just that in the barrel after you ream it out some, but that camera on the board looks like it's on an angle and probably for a reason. You'd have to duplicate the same angle. What I am saying is anything can be done, but not everything is easy.
The simplest way would be to get a gun with a plastic silencer and mod the silencer to hold the AimTrak. Now, even easier than that would be to get a light gun for the PS2 or xbox and just mod that and use the existing buttons and hardware. The barrel is already made for a sensor, so it should be pretty easy. I've seen lightguns modeled after the P99, Colt. 45 automatic, Berretta, Desert Eagle, Sig... there are lots out there and they all look pretty good. You can even find the exact gun that EMS TopGun gutted and modded for their gun! (And people still say the TopGun was totally engineered new from the ground up!)
Where Airsoft will work and work good is with the AEG rifles! There is a ton of room inside them too. You don't want or need a high quality AEG, actually the inexpensive LPEGs will be perfect. The site I buy a lot from is airsplat.com. People that buy a lot of airsoft know that most sites (not all, nothing is ever an absolute) get their inventory from airsplat in the first place!
I have pictures of all my guns in another thread on here and some would be really cool light guns! I too was originally thinking of using airsoft pistols, but that was also back when we still didn't have a viable gun so nobody knew what size components we were looking at. Now we know.
lol Now someone is going to go out and make an airsoft springer pistol work just to show me wrong! Hey, I am not saying it can't be done, just saying it will take a lot of work to do.