I used to buy Major nuts to eat off eBay. You might check. Plop them in a raised bed and you’ll have super caliper seedlings in 1-year.
Pecans in raised beds require 24" of depth. I read a study one time. It was stated at that university that white rubber mulch in 24" raised beds w/o fertilizer is all it takes.
Or, grow in Treepots 12" tall or thereabouts. There are a few 4 x 4 inch (x) 11 or 12 or 12.5 sold thru Stuewe & Sons.
It doesn’t answer your question, however, I can confirm that no-one have I seen sells specifically Major seedlings.