It is actually a pretty easy job if you have the right tools and a steady hand.
Jewelers are your best bet since they generally have the tools and the skill.
Some machine shops may also have the right type of files and a guy with the steady hand and attention to detail required, but that isn’t universal; it really depends on whether that shop does tool-and-die work (more precise than regular machining and with a lot of precision hand-filing) or not.
Some of your hard-core hobbyist model makers may also be able to help you.
However, I think the jeweler is the easiest to find and thus your best bet. At worst they should be able to point you to someone who can/will do it.