We plan to hold a National Collection of MTB's, the first we think, and according to records we're right. There are just over 30 in the 08/09 RHS plant finder so that means about 27 minimum in the collection and 3 of each rhizome.
I have located them in the UK by luck more than anything. And furnished with the warnings of the growers that "they don't sell" I am buying as many as I can!
Once we have them I will post pictures of each one included. but for now here's my first sprouting Iris of the season (above)