I've been making model graphics for years.
I don't make "decals" but many of my customers order cut vinyl graphics and lettering in metallic. They also order a vinyl that resembles "Metalflake."
Some say they clear the vinyl.
I'd make "decals" if I had a source for the "material." I've never looked into it.
The art is relatively easy, because I do art all the time.
If someone would provide a source for decal paper, or send some sample sheets, I'd probably start doing them.
I've been in R/C for the last 30 odd years, I just started up in CL, so I'm actually a bit unfamiliar with what's used for graphics?
Because I paint my models, I'll have no choice, I gotta come up with something.
Currently, I've always used a combination of "mask," hand painting and spray painting, both with jam guns and air brush.
I did this model in the mid 80's. Took a Best Finish at the WRAM.
This is my website: cfcgraphics.com