Here is another company that offers a lot of seedlings for sale. They are both a wholesale and retail company. They have a broader selection of seedlings then my previous post. How about some Crabapples, Beech trees, Hornbeams, Alders, Conifers, Black Gum (Recommended by me), plus a lot more.
Cold Stream Farm: Seedlings
Well I actually have purchased only bare root Nanking Cherries and I planted mine in a 1 gallon plastic with a tile under them, using turface, red volcanic rock and mushroom compost. There was an earlier discussion about your question and you can read it here:
https://www.rmbonsai.org/forum/rmbs-forum/kaedebonsai-en-seedlings
I bought some bare rooted prunus ume from Bill Valavanis and they died immediately on me. Most of my seedlings were in small pots, Good luck!
Mike, would you be able to share how you normally treat these bare root trees when you get them?
Plant in ground or pot, soil makeup, etc?