I bought mine from a local exotic plants seller that has other citrus. I assume they were seedlings, 12-18" tall and scraggly, they didn't look grafted. I'm not sure why they died, they simply never thrived and slow-declined into death over six months or so. They were fruiting at such a small size so its possible they were cuttings, or they may be very precocious. I never knew much about them to be honest.
If you find a good source of seeds let me know, I might try growing them again.