Multi grafted fruit trees

Is there a go to person for this? I was once set up across the way from an ag center that was hosting a rare fruit tree growers of the Central Valley in California. Like 200 different scions of apples, citrus, stone fruit etc and the guy leading the thing had an avocado tree with 50 different types of avocados on it.

Also, has any ever bought a tree that was shipped to them