There is a hybrid that is much more viable with larger flowers.
http://www.ces.ncsu.edu/fletcher/staff/tranney/ranneyetal.pdf

Forest Farm has some for sale, I almost ordered one this spring.

They list 3 to 4 feet at least.

Here is a link that might be useful: Forest Farm

Rare Find Nursery (www.rarefindnursery.com) has some although I don't know about the size. Greer Gardens (www.greergardens.com) does have them in the size you're looking for. Any 5 to 7 foot tree is likely to be very expensive to ship because of added "oversized package" charges. If there's a good nursery near you, they might be able to order one for you.

Johnny6, read up on the Franklin Tree and make sure that you can give it what it wants. You might check out the ancient Franklinia thread on the Botany Forum.
Why not slip down to Phily in May and pick up a plant directly from the Bartram's Garden?

Here is a link that might be useful: Historic Bartram's Garden

Thanks for all the suggestions. I found a nursery not too far from me that had 6 trees, 5'-6' tall. Rosedales in hawthorne.

looking for the new hybrid franklinia thanks

lee_7, I can't help you much, but some of this may be new to you. This is a working version of the non-working link from the second post above (the academic paper about the hybrid):
http://www.ces.ncsu.edu/fletcher/staff/tranney/ranneyetal.pdf

Here is a Google search for the hybrid by name:
http://www.google.com/#q=%22Mountain+schimlinia%22&hl=en&prmd=ivns&ei=0KAyTf2qBoOglAe2krizCg&start=10&sa=N&fp=fd0f73886609171d

The GW Botany thread alluded to above is here:
http://forums.gardenweb.com/forums/load/botany/msg0814324024340.html

Here's another NCSU article, this one from 2004 and not academic but for the nursery trade:
http://www.ces.ncsu.edu/fletcher/programs/nursery/mountainschimlinia.pdf

If all else fails, you might try contacting some of the names from the two NCSU papers. Or call NCSU Fletcher and see if anyone there knows what's going on with the hybrid or can suggest who you might call or email.

Good luck.