Just to restate, I beleive the answer is: there is no way as of yet to make your own sheets other than buying a custom order from a company that makes them. Not a cheap route.
The first I've read about anyone making their own was in the last issue of Pastry Art & Design when in an article they mentioned that one contestant in the 2001 best pastry chef competition did create his own transfer sheet using scanners. But the article said as of yet know one else knew what he was doing.
The closest thing you could do is silk screen onto a actate sheet colored chocolate or a glaze of some sorts. Let set, then spread contrast chocolate over it. The closest reference I'm aware of would be in Pierre Herme's professional book.
