Steel Guitars of nashville used to sell the big decals that go on the front of Stringasters and similar but once Bobbe Seymour passed away, the new people seemed to stop carrying them.
The one you are looking for is this one, I think. Since they were only ever used on the steels, it would be pretty rare to find an original, unused, one somewhere (and if you did it would probably not be usable any more). There are plenty of people, I am told, that make fake Fender decals and maybe one of those guys could be persuaded to make one with the added text. It's about the only way you'll get one but, of course, since it infringes the copyright of FMI and their lawyers are very touchy about that sort of thing I wouldn't recommend or encourage you to do this.
They are pretty much the same as the ones you'd get on a Strat or a Tele (but they don't have the Fullerton text).