I just answered my own question. I found a lovely one at Orange Garden Supply and it's being delivered this afternoon. They have 2 left (they generally get 5 per year).

What price might I ask?

Not cheap. I paid $325. Big splurge for me!

I'll continue trying to grow this one from seed!

I saw one today at Great Swamp Greenhouses in Gillette for $189.

There will be Stewartia at the Rutger's Garden sale this weekend, May 7 & 8.