Hi Jo,
I used a set of Russian made cutters. They are available on ebay, posted from Russia or the Ukraine. They are available from Mod 0.3 upwards in 0.1 intervals.
I've got 0.3, 0.4 and 0.5, remarkable value at around £32 for a set of 8 and the quality is really high. The larger Mods are a bit more expensive.
I also have thread forming tools from the same supplier in M1, M1.2, M1.4 and M1.6. Again, great price at around £14 each. I made hundreds of screws using these.
The prices include postage which is surprisingly quick.
Steve