Rudolf's advice is very sound. Most vendors don't have everything listed in their web-shops - I gather, they have to have a larger stock of a plant for the effort to be worthwhile. So it always pays off to ask.
If you deal with Hilmar at Asendorfer Oz., make sure, that you get a plant of the size you want. His plants are of good quality, but a lot of his Paph-sortiment is made up of young plants in 7 cm pots (my patience - maybe also my age - doesn't work very well with buying plants of that size). But Hilmar is always friendly in communication and his answers straightforward.
You could also try: Orchideenhaus Asien in Schloß Holte-Stuckenbrock (they have a larger sortiment, than can be gleaned from their homepage - and VERY reasonable prices!).
Another option is Franz Glanz at Wößner Orchideen.
If you want to be sure of getting a masterianum, write to Sam Tsui of Orchid Inn (
Paphiopedilum - Species - Page 8 - Orchid Inn Ltd.) and ask to be put on his mailing list to get informed when he visits Europe next time!