How far north in Texas would be far enough north for sourcing Quercus fusiformis acorns to grow at the Zone 7a/7b border in Middle Tennessee and stay green in winter?

[L.A.M.]

How far north in Texas would be far enough north for Quercus fusiformis saplings sourced from there to survive a USDA Zone 7a/7b transition Middle Tennessee climate and stay green in an average winter? It’s hard to come by ones sourced from Oklahoma which are reputed to be cold-hardy to -10 °F, and I’ve been told ones sourced from the Alamo in South Texas lose their leaves at 10 °F just like the coastal Quercus virginiana does. The guy that has one with this sensitivity is sure they were correctly labeled because it came from the iconic one at the Alamo and the acorns are more fusiform than the coastal southern live oak acorns are. In fact, I’ve been told Q. virginiana sourced from Virginia keep their green leaves down to 5 °F in Tennessee!

[Zeeth]

Try the ones from Alligator Alley Nursery:

https://www.alligatoralley.com/mailorder.html