I'm not looking to buy anything right now, but was looking anyway. I found a nice shotgun that looks like it would make a good gun to convert if someone was looking for a gun right now. Its a Mercury made by Zaballa 12ga with 3" chambers and in the pictures you can see it has a third fastener, a Greener type I believe. Just thought I would share that if anyone was interested.

http://gunbroker.com/Auction/ViewItem.asp?Item=77635613