http://www.countryarbors.com/ might have it. I can't tell which two they have.

The National Arboretum has it. Perhaps you could get a cutting.

Hello Rhodyman, thank you for the link! It looks, however, like what they have is an R. Poukhanense. How would one go about getting cuttings from the National Arboretum (short of showing up with some scissors :))?

I would contact them and ask if they know where you can get the plant you want. Tell them you know they grow it but don't know where to get it. For a photograph taken last year at the National Arboretum check

http://zipcodezoo.com/Plants/R/Rhododendron_yedoense.asp

Here is a link that might be useful: National Arboretum

Hello Rhodyman: What a great picture! you certainly do know how to find things. I wonder what they mean about it being "invasive." If only my privets and bamboo had flowers like that! I had looked at their site after you first told me about them and they have a policy of only giving out "germ plasm" to researchers and some (presumably also researchers) individuals. Kind of a high bar for me. But I really do appreciate your suggestions. Thanks!

Invasive means it spreads. It is stoloniferous.

Van Veens Nursery in Portland, Oregon, will root cuttings. It might be worthwhile to contact Kathy Van Veen and see if she can get some starts for you from the National Arboretum. I believe she qualifies as a researcher. If they are not in the general trade, perhaps this would be a way to get them there.

Here is a link that might be useful: Van Veen Nursery

Hello Rhodyman:
So, it would spread in much the same way that some native azaleas do...that would mean square feet not acres, right? Not like kudzu or bamboo which can eat your entire domain in a year. This is what I meant by questioning their idea of what is invasive.

I would like your take before I go any further with this...Kudzu and privet have wonderful smelling flowers but they are certainly not worth the headache the rest of the year. I simply cannot believe that people spend actual money on privets; that they consciously BUY them. I'm quite sure that whoever invented agent orange had them in mind.
Mike