Sir, can you get me a pawpaw?

Do you really want a pawpaw?
Asimina species

Why aren't these common in the nursery trade?
1. You need two trees of different varieties to cross-pollenize.
2. Crushed leaves smell like diesel fuel. Mmmm.
3. Pollinated by carrion flies and beetles, the flowers smell like rotting meat. This alluring idea comes from a web site: “I have hung chicken bones to attract carrion flies to the flowers, and others have used this practice to improve pollination.” Or this from Wikipedia: “Growers of pawpaws sometimes place rotting fruit or roadkill meat near the trees at bloom time to increase the number of pollinators.”
Charming.
4. The fruit flavor is low-acid, often described as like bananas or custard. It ripens quickly, with a soft texture. Each fruit has numerous large seeds, so it is mainly eaten as pulp. If they are pollinated and pollenized correctly, yields are high. Imagine large amounts of custard-like fruit with very short shelf life all ripening at once.
5. The trees are tap-rooted and the roots are fragile, so they aren’t common in the nursery trade; trees with those characteristics have notoriously high failure rates.
So no, I probably can't get you a pawpaw. Perhaps the great folks at ForestFarm in Oregon can help you out:
http://www.forestfarm.com/product.php?id=635