Garden Railway Specialists do a waterslide sheet. Need trimming out as the individual decal's carrier film is not separated. Found them a little thin and difficult to handle. Suspect a miss-applied laquer coat on particular stock bought. I had problems with enamel/thinners satin laquer dissolving them. You will need apply to a gloss base colour coat if you are going to "hide" the carrier film.
Could try DJB, although they say they have stopped production, as they may have left over stock. Thiers are very good qulality two colour (gold with black drop shadow) dry print and work very well, they also do the "smoking/no smoking" window signage. Did my rake of GRS L&B coaches with them.
I have some leftovers of both, which should be more than enough to do your railbus, if you would like them. PM me if you are interested.
Max.