It may also be worth looking at a tension file that fits in a standard hacksaw frame. This blade will cut in all directions, and with care can cut all manner of irregular shapes. One brand, many years ago, was Abrafile. The teeth were graded from very fine to coarse from the handle end which made starting each stroke very easy. Not sure if they are still available.
I recall also a tool like a drill bit that fitted in a drill or Dremel. It had a helical form so cut as it rotated. The name escapes me at present.
BT