You don't list where you live but I do see your hardiness zone listed as 8. Are you planning on trying to grow these for fruit in zone 8?

I would seek info on loquat rootstock supplier on the Tropical Fruits Forum.

Here is a link that might be useful: Tropical Fruits Forum

Loquats do fine in mild temperate zones - they're all over Japan.

Grafting from the mature fruiting tree onto seedlings should speed up the process a bit.

But loquats seedlings don't take a long time to bear fruit anyway. I would guess they'd fruit in they're 2nd or 3rd summer if pampered a bit.

Also, the fruit will tend to breed somewhat true to type, as they are not as hybridized as many of the more common fruits.

Thank you for the feedback. I will take some time and do some more research. Your responses has given me more options.

Below is a link to what I think is a pretty good source of info about loquats (particularly regarding where they can be expected to reliably produce fruit).

Here is a link that might be useful: from Fruits of Warm Climates by Julia F. Morton