I have been very happy with a lot of pre bonsai I have purchased from smaller independent sellers on eBay. You need to be discriminating when shopping there but I have some fabulous plants. Point in case, I have balsam fir, white spruce, hemlock and such that I bought from a small collector in Main. I have half a dozen 35 year old Korean Hornbeam from a seller in Maryland. I have purchased pre bonsai and starters from most of the east coast states. You need to be vigilant and look often because most of these sellers only offer a few plants at a time. They almost always combine shipping.
For online, it is hard to beat Bonsai Jack for soil components.