Try the Trees and the Fruit and Orchard Forums.

Also, try asking your County Extension agent - if he/she has no personal knowledge, the office should have handouts/publications. Your state Forestry Division MIGHT, as might your state university. Try Googling for WI, nut tree, orchard, and see what you get.

Hope these are helpful, and not what you have already done, to no avail!

Check out info at the Northern Nut Growers Association website; I don't see a WI NGA listed, but there may be NNGA members in WI - and members of NGAs in MI, IL, OH, may be able to help you with advice &/or recommendations for reliable sources
Those NNGA members won't steer you wrong - and some of them may be a good source of plant material for you.

Here is a link that might be useful: Northern Nut Growers Association

St. Lawrence Nursery in New York carries all kinds of trees for cold weather. I forget their address, but you can google them if you want.