Well I can provide seed.
I agree , their is potential here, but this is quite the project .!
My trifoliate are outside and very hardy, but the bloom times don’t generally overlap with my indoor variety collection .
So I have not made crosses.
It would be the potential crosses that you would want to grow out for evaluation.
This is a very thorny project.
Maybe best as a perimeter hedge / fence. And would make a VERY impenetrable fence.
Would require a excavator with steel tracks to remove.
Maybe growing out seeds from a trifoliate from the south ,that was surrounded by other good varietys for pollination would be easyer. Most seedlings will be nucellar, and identical to the parent
May be able to select promising seedlings by leaf shape befor they fruit?
I have a collection of the hardiest citrus / hybrids I could find.
None of which have been hardy out side here ,zone 6 Wv.
Whith out protection. Thomasville has survived several years outside befor dying.
My trifoliate are hardy and productive, just to bitter to use.
I do think there is potential for a cold tolerant citrus,
Good luck