I searched the part # to find it & posted the first hit I got – I’m sure you can find the same thing (or similar) for less. I bought mine at Ocean State Job Lot for $1 a few years ago, to use on a cordless phone handset. It’s a 2-pack of plain black plastic clips that attach with double-sided tape. It’s a little longer than the Sansa Clip, but it’s just a piece of plastic (cut at your own discretion). I used 1 of the 2-pack, and the other is still in the package (that’s where I got the info to search). The clip itself is marked “The Clip Co.”, but the package says Southwestern Bell S60179.
Personally, I think the other link I posted is a better option – and should be available locally at a Walmart, Target, dollar store, etc. That one is a plastic button that gets attached to the device (your Clip) with double-sided tape, and the button clips into the belt clip (sturdy, quick-release, swivel, and easy to get on & off whatever you feel like clipping it to). The one I got also came with a separate piece that I stuck on my dashboard, so I can hang my phone there instead of on the belt clip while I’m driving.
Hope this helps.
Btw, great job with the homemade!! I like it!!