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.
Uh oh. Gotta go. Here, you read this tiny ad. Bye!
try a month in the "gardening gardeners" program to see if it soothes your soul