Sorry to hear about the problems with your project, HH.
Vinyl decals need to be of the correct material to be paint and/or petrol proof! Any decent decal maker SHOULD be able to produce something if you can provide an image with correct sizes and let them know it will be lacquered or may be subject to exposure to fuel.
The obvious alternative is, of course, to stump up the inordinate cost of a genuine Triumph item!
Good luck with it - hope it gets resolved satisfactorily.