I strongly recommend JL Hudson:
http://jlhudsonseeds.net/ I know that he offers
black Locust and Siberian
Pea bush/Tree. Probably several others.
I have dealt with him for years, and never any surprises! They are in their 100th year, and the present Owner/Operator has been there about 40 years.
His prices are quite reasonable. Order 1 or 2 packets from him and he will send you a catalog (all seeds listed by their Latin names). with your order. The catalog is a great reference book on plants.