I use the plastic strapping that they put around heavy packages. I used to have a whole box of it. I had to have it at one time for bulk mailing for the PO which they didn't use for long. I thought I'd kept the box but apparently I must have gotten rid of it or it's well 'hidden' in the netherlands of my sewing room. I think this was 1/2 in wide. I think I still have some rolled up; you only need the amount to go around the top of the thread catcher. You might check with some of the big bulk stores and see if they have some that they've cut off boxes that they've gotten merchandise in. I'm sure they'd be glad to get rid of it. If you can't find it; pm me and I'll see if i have some and will send you some.
For the weighted filling I used very fine (clean) play sand in a heavy duty zip lock bag. Seal it up and squeeze out as much air as you can; then I taped the edges down with like clear shipping tape and slide it in your sleeve pocket, tape side down. The fine sand is also great at sharpening the pins.