Look at the URL   http://www.sssink.com/var.html

which describes how to mount the decals, but also claims that the
Duplex Decal Stock (consisting of a heavy layer bonded to a layer of
tissue paper when is them coated with dextrose gum and on which the
desired image is printed upside down) is no longer made but the company
claims to have some stock left.

It appears to have originated in Europe for applying decals on bicycles
per this source, and the paper may have originally come from England.
Perhaps it still does, but if so, none of the several search engines
I use has found a web source.

Regards,
Henry Holifield
hohueben@eden.com