I wouldn't even worry about grafting mulberries, they are easy enough to grow from just shoving cuttings in the ground that your grafting time and dollars would be better spent on pears and apples IMO. Find a prolific producing mulberry tree, take some cuttings and shove them in some soil(whether it be in pots to get them started as bare roots or planting them directly into their final resting places) and let nature take it's course. Finding improved rootstocks for mulberry could be a daunting task as well. One other huge consideration that I have read, but have no verification of, is that you must know the "sex" of the rootstock before you graft to it. I have read that if you graft to a male rootstock, you will never get any fruit, as only female mulberry trees produce fruit. Try to get your hands some "Northrop" scions, SLN used to carry them.