Small amounts of rootstock seeds are a challenge, especially from a foreign country.
The 812 is available from commercial nurseries in FL, but I was only able to obtain grafted trees. My grafted portions all died due to frost and this year was a very cold year, so the rootstock may have died. If it survives, I should be able to get seeds in a few years.
Large quantities of seed are available for research purposes, but there are some agreements you would have to sign to obtain them, and I highly doubt they would be shared outside the US due to the low enforce-ability of international agreements.
If you want to buy grafted trees and deal with the challenge of importation from FL then this is possible.