I’m looking for a source of R. maximowicziana (plant material or seed). It was available from Dr Berkutenko’s seed list but I have been unable to contact Dr Berkutenko and have found no other source for this species.
I don’t want to stray from your request, but if you can’t find a source of R. maximowicziana you might want to look at “White Mountains”. It appears that WMs is a seedling selection of R. maximowicziana via Skinner’s Rambler.
Rosa maximowicziana is at Kew. It’s in bed 185-09. Go strait into the field in front, directly opposite the entrance. There you will find a whole series of island beds filled with species roses. It isn’t on the map. The map only shows the rose beds surrounding the palm house. Next time your in London I’m sure you would enjoy seeing all the species roses they have.