You could try EBay.

Mckenzie farms or ediblelandscaping. Both have websites. You'll be able to get a much larger plant than a seedling in both cases. If neither have poncirus in stock, you can buy a cheap tree from either that is grafted onto poncirus and just cut back the grafted tree and let the trifoliate rootstock grow. That's what I did and it worked out fine.

benjoe,

I have some poncirus fruit in the fridge that I will be opening in the spring. Hopefully, they have seeds in them. At that point I could hopefully send you some seed.

Kristopher