I have a handful of rolls of 3M #235 BLACK PHOTOGRAPHIC TAPE to sell. It's more than I'll ever use myself so I'm offering it here. This is a paper tape similar to masking tape, except it is opaque with a black flat crepe surface. I've used it for trim on tubing when I didn't have endrings, as a spacer around sub-diameter eyepieces, and anywhere I needed a flat black surface.
1-roll/1-inch X 60 yards...$10.00 postpaid in CONUS. (retails for $19-$23 from graphic arts suppliers)