We always called those Hartco guns, now I know what you're talking about. Stanley bought out Hartco. Those are good for attaching springs to border wires and tie wires. Not easy to find used ones, but here's a link: CLICK HERE
I thought the belted clips would be a lot more than they are, but they're only about $60 for a box of 3,600. Here's a link for them: CLICK HERE
Use the paper lined steel clips, they are quieter and hold better.