I would say the same thing. Make, or have made, decals.
I don't know about UK but all of the buses I see have skins for advertising. A bit like a giant decal really.
The issue would be transitioning to the roof.
Looking at Rocky, you could paint the colours (green, red, blue, yellow) masking in the usual way, and then use white pinstripe tape (used for car paint jobs) in between. That will allow you to do the more fine lines with ease.
The black text you could print yourself with decal paper, but white decal paper would require more careful trimming for the white text. You might be better getting those few decals produced professionally.