Apple grafting newbie question
I am an avid native plant /prairie gardener, and an enthusiastic (if not always successful) veggie gardener. I recently discovered heirloom varieties, and I would like to start a few semi-dwarf heirloom apples in the back yard. I can get scion wood, but I cannot seem to find a source for rootstock. Is there a code word that I am missing in my google searches? Any recommendations for a good source of apple rootstock?
Also, I was planning to chop down a crab apple tree to plant the heirlooms. Might I be able to graft yummy heirloom scions to the crab apple stump?