It sounds to me that the decal you saw was likely custom made, and not mass produced.
My place of business does repositional vinyl work (decals), primarily all of the Fathead business, and I know the Fathead site that feeds into our printers allows for customization. However, for a small custom run, we typically will send them to sites like Etsy, Vistaprint, Cafe Press, etc.
You'll end up paying quite a fee for only a one or two decals, so if you cannot find these elsewhere, and really want to get yourself one, I would recommend trying to find others to chip in with you to buy in bulk, say 50 or 100. The setup charges and handling make up the biggest portion of the price, and the individual decals are practically nothing at all.