If you can find a graphic somewhere online, you can download it and then print it on "decal paper." You then give the decal paper 2 coats of clear spray paint, cut them up, and apply like any other decals.
Not as easy at that.
Decal paper comes in white and clear. If you use clear, then apply the decal over a dark painted surface, the decal does not show up well...
If you do wish to make your own decals, you might need to use a printer that includes white ink.
If you can find proper examples of what you want, complete with really good pictures and measured sizes, Greg, at Cyclomondo, will make you a set for a price. He does really good work, in my opinion.