You might try this site http:__www.almaco.com_ Their products are actually for research plots but some of the stand alone threshers might work for you since you have a small area, but you would till need a way to cut the beans and get them to the thresher.
I know where there is a platform with a 22'Sund pickuup on it, platform has perforated floor in middle section to let dirt out. Sale date is March 3, Goodland KS.