I was able to finally get to a Joann's Fabric store today. Looked through a lot of black material which I felt would not work- either not woven tight enough to be light-tight, too thick, not lint-free, or too stretchy.
Finally decided to try a Velvet Ribbon $5/yd, 100% nylon, 1.5" wide, stock #07865488. It is just a little thicker and wider than the original felt but otherwise seems like it will work. The original felt was 1 3/8 wide.
They also have something called Neo Emp Velveteen at $14.99/yd roll stock #01581974 (mostly cotton) which might work: I might try that as a fall back if the ribbon doesn't work.
It may take me a few weeks to get around to putting these together, but I will at that point report back.
As someone elsewhere has suggested, I'm going to try just pulling the existing trap out of the crimp then use a wide flat blade to pry it open for reinserting the trap with new felt. It seems like a simple procedure, but the proper tools and technique will be important to make it smooth working- so I'd appreciate any input from folks who have experience doing this...
Keith Ostertag