We tend to think that nurseries like Stark are making a living by producing and selling to the retail market alone. But most large nurseries probable make most of their sales to commercial growers who plan ahead and order 1000's of trees on a particular rootstock a few years ahead of time. The homeowner or hobby orchardist is a niche market. Whatever the Retail Nursery happens to graft or whatever is left over from wholesale orders is what we, the retail buyer get to choose from. Because of the ever-changing possibilies of rootstock grafts and varieties if would be a monumental task for the Retail Nurseries to keep track of inventory. For a nursery to graft every variety onto every rootstock to make the Retail Buyer happy would inevitably lead to too many trees never being sold at a decent profit. And even doing that they would sell out of the prefered varieties on the preferred rootstocks.
Nurseries are either Wholesale or Retail or both. Wholesale nurseries graft thousands of one variety and rootstock as a custom graft for commercial growers and do not sell to the retail buyer. Wholesale nurseries do not even graft trees for the retail market but will sell extra trees wholesale to Retail nurseries. (I don't know if Stark produces all its own trees or buys some wholesale. If it buys wholesale trees then they cannot control what rootstock those trees will be on. They buy what is available.)
Wholesale nurseries sell their extra trees to the Retail Nursery market who then sell to hobby orchardists and home owners. Therefore the trees available to retail orders are a mishmash of whatever is left over from wholesale orders. All Rootstocks cannot be guaranteed at wholesale prices.
Some retail nurseries will custom graft a custom tree for you (any rootstock onto any variety they have), but the price will be higher and the wait will be longer for your custom tree. Of course, if you have the time to go that route you might as well order your own rootstocks and graft your own trees.
I do not nor have I ever worked in the wholesale or retail nursery industry, but this is what I have gleaned from talking to nursery owners about why they do not advertise the rootstock type on their apple tree orders. Usually all that is advertised is that the apple tree variety is "dwarf" (B9, M7) or "semi-dwarf" (M106, MM111, B118), and there is no guarantee of the actual rootstock used. Sometimes if you badger the nursery they can tell you their best guess if they look at the actual tree they are selling you. The trees they are often color-coded as to rootstock type.
Therefore if you absolutely REQUIRE your apple tree on a known rootstock due to environment or climate, graft your own.
