The tape I was originally looking at was Line O Tape. It came in widths as narrow as 1/64, lots of different colors, and masking tape. It used to be readily available from hobby dealers. I don't know if it is Covid related, but in the last few months it has disappeared.
The only thing I can find now in the very narrow widths now is "chart tape". Apparently it is used for making grid lines on white boards. I was wondering if anyone had tried it for masking.