I've used Whitman farms for grafted japanese maples cultivars that need airlayering. Lucille is very nice! They ship but it's not worth it unless you get a few.
Natures way in PA is great for pre-bonsai. Not sure if they ship. Worth the trip.
High quality prebonsai seedlings cultivated in the United States.
kaedebonsai-en.com
I should add that almost every club I've been to has a member that has started a nursery or ground growing project that has gotten out of control. I always keep a shovel ready to 'help out'. '