I don't know anything about grafting, but how would you graft a tree to another if the first is matured? I think grafting is done when the trees are very small and a like size piece is grafted to it? I think you would be better off buying a tree that is compatible for pollinating the one you have and planting it close by. Not just any pear, it needs to be one that blooms the same time as the one you have. Some bloom early season, some later season.
A great place to learn about fruit trees is Grandpa's Orchard.
http://www.grandpasorchard.com...
