Does anybody know a source for this species Rhododendron, preferaly in the northeast?
Too bad you didn't look for it earlier.
Roslyn went out of business and was selling everything, including odds and ends.
When I was there in early June they had couple of 15 to 18" (not so well grown, though) plants. I'm sure they are gone by now, but it might be worth to give Roslyn a call anyway, if they are still operating.
Try Rarefind nursery in NJ. They have an excellent website and will quickly respond to special inquiries via email. I am pretty sure, though, that what used to be known as r. smirnowii has been reclassified and has a different name.