I've bought about half of my collection online but its the more significant half...
In Minnesota we don't have bonsai nurseries, I have taken to trying to encourage friends and other club members to open one and assure them that I will be a customer.
my tip would be to search the suggestions of bnuts and then look at those businesses, some like Andrea at Wigerts are happy to answer the phone. Generate a good selection group of potential growers and dig in.
My fav online seller I mentioned in a previous thread of mine, bought several trees from him over ebay, now we text and I get a discount, after reaching out he was more than happy to be more personal