Jackson and Perkins is a legitimate company. Is that who you are talking to? I know they graft their own roses but I suspect not the avocados so they may not know what the root stock is. Per your original question, I would buy a tree outright. You will only find scions if you know someone with a tree. Its been an interesting conversation in between though.
Here is what the University of California says about Wurtz:
https://mgorange.ucanr.edu/Edi...
Growing in containers - "Little Cado" dwarf avocado tree
The Wurtz avocado tree, sometimes referred to as Little Cado, is the only true dwarf variety of avocado and will consistently produce good fruit from May to September. Compared to other avocado trees, which can grow up to 80 feet, a Wurtz avocado tree grows to about 10 feet. Due to its small size, the Wurtz avocado tree can be grown in a large container (such as a half wine barrel) and is a good option for smaller front and back yards. The Wurtz avocado is a hybrid created from the Mexican and Guatemalan avocado species, and produces abundant fruits within one to two years of planting if it is a grafted tree, grown in the right conditions and properly taken care of. This is the best Avocado variety for containers.
A Wurtz avocado tree will do well in mild-winter areas of California. Avocados like loose, rich, well-draining soil. Plant in a container that has drainage holes, in good quality potting soil. The soil may need to be sandy to accommodate the tree's large roots and fast draining so that the roots do not succumb to root rot fungus. Avoid manure-based mixes, as these have a tendency to be too salty.
Dwarf varieties in containers need frequent watering, perhaps even daily during the summer months, to keep the soil lightly moist. While the Wurtz avocado tree can tolerate temperatures as low as 25 degrees F, it should be kept in a warm environment as much as possible with protection against strong winds and frost. A young tree, one that is less than 12 months old, requires shelter from direct summer sunlight or the stems and bark will burn. After a year or two, the tree will grow enough foliage to shade itself from the sun.
Fertilize with a well-balanced citrus and avocado food on a regular basis. Frequent pinching of young tree stems helps to keep the tree in the desired shape.
Flowers
If the Wurtz avocado tree is cared for properly, it will start growing flowers for pollination sometime between January and March within one to two years of planting, if it is a grafted tree. A grafted tree is a tree grown from seedling tissue that has been mixed with the tissue of a producing tree. Purchasing a grafted Wurtz avocado tree from a nursery is the easiest way for the home gardener to have a fruit-bearing tree. A tree grown directly from a seed will not start producing fruit until it is 8 to 20 years old.
Fruit
The Little Cado bears young. Once the flowers are pollinated, the Wurtz avocado tree bears fruit that ripens between May and September. The fruits are dark green and medium in size, ranging from 6 to 12 ounces. They have thin, shiny skin with small seeds. The fruits have been rated by growers as having a good and consistent flavor, with an oil content of 16 percent. Avocadoes will not ripen while still on the tree. Harvest when fruits are of mature size and still firm. They will ripen in one or two weeks at room temperature.
