Timber Framers Guild Forums General Barns and Traditional Timberframing Number of traditional timber frame buildings?

Greetings all - I'm new to the forum - doing research on timberframe construction, and I'm trying to come up with an estimate for the number of traditional timberframe structures in North America.

The National Historic Covered Bridge program has a survey of covered bridges (800), and the USDA has a census that 650,000 farms with buildings from before 1930. The National Historic Register has 88,000 structures, 8,000 contain the word "timber" and 1,000 contain the work "mortise".
I'm wondering if anyone knows of a database that might assist in determining how many of these buildings are out there?
Thanks

try getting in touch with someone at TTRAG.

Traditional Timberframe Research and Advisory Group

I know they survey old structures.