These are some of the broaches I made and used many years ago. one of these is 48 years old. I made it in 1961. when I was making my own locks.
All you have to do is file a tapered square and file teeth on it with a three cornered blind file. The teeth then need to be relieved a tiny bit with a stone on the cutting edge. Drill your minor diameter hole. In the hammer then push the broach thru it in a vise, drill press or lathe. I use a rod with a hole drilled in it to keep the broach in alignment until it is started real well. Broaches now cost around $100.00 each. I am now too old and lazy to make them so I buy them now. This is way better than filing them. This is how the old gunsmiths did it. I saw some of these in the tools from an old gun shop from about 1850's in the Dalles Oregon on the Oregon trail.
Thought some of you guys might like to know .