Unless you want to hand grind a single point cutter, you're going to have to spend money.

I'm pretty sure I found a site that was selling them for about £40 a cutter, but I can't remember where.

You could also turn a bit suitable hardenable steel the correct pitch (remember thread mills aren't 'threaded' they're a series of rings), shape it, harden it, then grind to sharpen it.