Stan Mckenzie Farms in SC. He is out for now but he could have some this fall or next spring so you can email him:
http://mckenzie-farms.com/
As guys like me grow it out, scionwood will become more available so it wouldnt be bad to start growing some trifolate or Dragon rootstock for grafting 
Stan also told me Prague is hardier than 10 degree tangerine. And it is more the taste of a tangerine. But both are good and both survived Stan’s damaging 8F blast that killed many of his satsuma etc.
Here are some copies of fb posts on it:
Here is a blog post with lots other info on it: