I have a total of 5 light guns I picked up in a group buy a while back. Any one of these would probably work well for an AimTrak setup, or you could just buy it because you need it for your console.
From left to right in the photo:
1. Namco NPC-106 Gun Con PS2 light gun
2. Logic3 P99G2 with recoil and GunCon adapter (not pictured)
3. Performance Lightblaster for PS1
4. Naki Uzi PS1
5. Nyko Super Cobra for PS1
1, 3, 4, and 5 are all $5 each. The Logic3 (the one with recoil) is apparently pretty desirable, and I'll likely sell it on eBay. If you want to make an offer on it here, feel free.
Shipping should be pretty inexpensive. These should fit in a flat rate envelope. I'll be happy to offer a discount to someone who wants to buy the whole lot.
Thanks for looking!