You may want to see about any Ag Department databases or native plant society databases. I haven't specifically found what I was looking for with food bearing trees, but I've seen what kinds of tree families grow in the area and then I've researched their food-bearing relatives.
To get a wish, you need a genie. To get a genie, you need a lamp. To get a lamp, you need a tiny ad:
Our PIE page has been updated, anybody wanna test?