A friend's redoing his '82 Turbo GN and he's getting the decals done. Once they get them in thier computer, they can pop out more. If you have an old decal, you send it to them and they will redo it. (I haven't done this personally, so I don't know all the details.)
Hard part is getting the old decals off somwhat intact.
http://www.osborn-reproduction.com/