cold hardy dwarf grafted avocado.
I see this is an old post from a few months ago, but just wanted to let you know that there is no such thing as dwarfing rootstock for avocados, and any nursery claiming otherwise is lying to you. There was a lot of research from the 1940s to 1980s trying to find such a rootstock, with complete failure.
The good news is avocados are generally amenable to aggressive pruning, so you can plant at high density and keep them small (8-10 ft) with heavy pruning.