Thanks for the question Bruce - and I believe I have the perfect answer for you! Depending on how "clean" the rows are between trees, the "Bag-A-Nut" should do the trick. Many of our seed collectors in Illinois use a Bag-A-Nut to collect oak, hickory, and black walnut seed. This device is extremely efficient collecting seed in parks, cemeteries, parkways, etc.
Check them out at http://www.baganut.com
By the way, many of the Soil Water Conservation Districts in Illinois have their own Bag-A-Nuts for loan to county residents.
Happy seed collecting!