I am sure there are folks that make stamps commercially, but if you know exactly what you want, our own David Crisali likes to make little things like that and might be able to help you out. Personally, I would try to make something like that myself. I have made smaller stamps out of 1018 rod (case hardened) and O-1 drill rod. The stuff I have made were easily accomplished with needle files and a square graver. I believe there is a tutorial here somewhere showing the process. Maybe someone else will remember where. I have also bought various style letter and number stamps from Brownells, Tandy, Amazon, and eBay. I use stamps for metal and leather. Of course the ones you use on metal need to be hardened, but barrel steel is pretty soft and they don't need to be real hard.