If you are looking for seedlings to practice with they can be bought here.https://marketplace.uidaho.edu/C20272_ustores/web/store_main.jsp?STOREID=57&SINGLESTORE=trueThese are pre-pre-bonsai but make for inexpensive practice plants.
Colorado State Forest Service does bare root and tube seedlings as well. Looks as though the prices are somewhat comparable.
https://csfs.colostate.edu/seedling-tree-nursery/buying-seedlings/