Greetings James:
I would encourage you to consult a professional forester regarding the sale and marketing of your black walnut trees. Selling high-value hardwoods via the "shares" method, as you've described, is generally considered a very unwise financial and forest management decision; unless, of course, you as a forest landowner are extremely astute in the evaluation, appraisal, marketing, and frequent sale of hardwood timber.
Since you're asking the question, I'm going to go out on a limb and assume that you are generally unfamiliar with many of the intricacies and nuances involved in sale preparation, marketing, and administration of a timber sale -- don't worry, 99% of Illinois forest landowners fall into the "unfamiliar" category.
Again, avoid selling your standing timber "on shares;" instead, contact a professional consulting forester today to assist you in marketing your timber -- you'll earn a lot more money and you'll retain more high-value trees for future timber sales!
IL Directory of Professional Consulting Foresters:
http://web.extension.illinois.edu/forestry/pdf/tfb-nres-202.pdf