USDA plant databases include distribution maps.

Most states have Native Plant Society chapters online.

Major universities in each area often have edible and useful plant guides online.

Herbal schools in many areas can steer you in the right direction.

Public park systems and museums in each area often sponsor or put on plant walks to introduce folks to the edible and useful plants in their area.

Bookstores in each area usually have the appropriate plant field guides for sale. Amazon online is always a good place to check.