why not use stickers? does it have to be electrical tape, industrial? Several places offer round stickers at all different sizes:
googled : round stickers
I`m sure you checked 3M, and I`m not sure about your specific app, but I`ve found this a great place to strart for a lot of "tape" (they`re the monster for a real reason) http://solutions.3m.com/wps/portal/3M/en_US/3M-SpecialtyTape s/SpcltyTape/ and they have vendor lists you can use too.
And I like this company as they have US and asian mfg (ask for Paul or Jimmy)
http://www.chuspkg.com/ ... they are friendly and will answer your quesitons (I`m not even sure if what you want is possible; maybe an overlay or built-up tape that`s opaque on a base product)
Hello Crutches!
Have you tried good ol`thomasnet?
http://www.thomasnet.com/browse/adhesives-sealants/tapes-1.h tml