This post has been on the back burner for a day or so... I've given it some more thought since, and found that if you look on eBay for "2mm Tap" you'll find a large number of jewellers taps, usually ranging from 0.7 to 2.0 mm in 0.1 mm increments. They're dead cheap too. No idea how good they are, so if anyone knows, please post. I started this as a new thread, sources of fine taps might be something we need an easy to find thread to cover, as suppliers change, they can't guarantee a regular trade in unusually small sizes, but we'd always have use for them and could share info on sources and prices. These things cost a bit if you want good ones.
What I was actually after was the high quality Dormer fluteless taps. M2 have 0.4mm pitch which is better than 60 TPI, and I've used the M3 and M4 versions, they're fantastic taps, they work-harden the tapped hole, make a fine smooth finish, and don't leave any swarf. These are ideal for hand-made fine optics tuning assemblies. They cost around £15 each or more, but considering the freedom you get for the money, one mount will be enough to pay for the tool.
Also worth tracking are good sources of cheap A2 and A4 stainless M2 machine screws, especially countersunk Allen headed types. RS Components (European) probably have them, but not cheap, and not everyone has access, you need a trade account.