I thought I remembered Christopher Schwarz mentioning a place on the East Coast (North Carolina?) when he was doing the Roubo Bench builds ...
But, apparently I was wrong:
https://www.popularwoodworking.com/chri ... for-hands/The above link talks about Cherry planks, but I recall him using some White Oak during a Roubo Bench built class. I'll keep looking ...
Woodfinder shows two places, but, as you have found they are a ways away:
"Woodfinder found 10 supplier(s) in our database
that match your search criteria:
Products, services or species listings include "OAK PLANK"
Businesses closest to zip code '77410'
Click on the company name(s) below to view their product listings and contact information.
Please tell them you found them in Woodfinder®!
AGINCOURT Hillsborough NJ (1387 miles)
Moore's Sawmill Bloomfield CT (1517 miles)"
ETA: Found it! Horizon Wood Products ... in, yup, Pennsylvannia.