I crave good chisels too. Sorry, couldn't help myself.
Most carving, especially relief carving, will be out of place on a SMR. Some incised lines might be appropriate depending on the school or area you are trying to emulate with your SMR. Incised lines can be cut in with a small V chisel.
Fortunately, there is a solution. Get one of Jim's colonial longrifles and carve it!
For relief carving, 5 chisels (flat) or gouges (curved) isn't very many, but could get you started practicing, then you can see what else you need to add. I use the following quite a bit:
4 mm skew chisel
2 mm 30 degree V chisel
4mm #6 gouge
2mm #8 gouge
4mm #8 gouge
-Ron