Actually you can buy tools that small, Bits & Bits sells them. https://bitsbits.com/ But you need to be able to turn them about 50,000 RPM. I use a cheap air pencil grinder in my spindle. I have run tools as small as 0.005 tip with good success.
As you say, this is normally done in a very tight punch press, but for prototypes this would be expensive to do. The punch & die is not that complex, but would require tight control of the shut height.
A ribbon die might be worth a look also.
Here is a picture of my setup, the grinder fits a 5/8 tool holder. Due to the design of my spindle, I can run the air line where the drawbar would normally be. But the air grinder could be set off to the side of the spindle on a bracket attached to the quill.