There's a nursery in southern California that will now ship avocado trees nationwide.
www.willsestatemaintenance.com I had searched around for about a year or so looking for someone with a good reputation who could ship Lamb Haas, Sir Prize etc.. but was just out of luck until I found Will Slattery. Finally someone who would ship to the east coast! He also has citrus and low-chill peaches too. Some of these trees come from Brokaw Nursery or Dave Wilson (wholesalers), but he has some deal worked out with them and is more than happy to ship to you. My 5 gallon trees honestly looked like 15 gallon ones. Shipping costs can be rough and CA adds an inspection fee, but he has access to some things we just can't get here on the east coast.