(see my earlier post with pictures)
Oops! I DID finally get a response from Willis Orchard and here it is:
Jay Young (firstname.lastname@example.org)
I am not aware of there being male and female mulberry trees. The mulberry trees here are dioecious and have both male and female flowers on the same tree. I believe you will need to wait at least another year or two before it will begin reliably producing fruits.
I hope he doesn't actually believe that...I have several examples of large old Mulberry trees in my own neighborhood that ONLY produce male catkins. Some people don't want fruiting mulberries because of the berry stains and bird droppings. Also, I believe Jay has diocious and monoecious confused...
Definition of dioecious
1 : having male reproductive organs in one individual and female in another
2 : having staminate and pistillate flowers borne on different individuals