Here are a couple links to Nebraska's Game & Parks website. The first one is an interactive map of public hunting grounds...the second is the main page.
http://outdoornebraska.ne.gov/gisapps/default.asp
http://outdoornebraska.ne.gov/hunting.asp
Also...here's a link to a guiding service that's run by my cousin. Check it out if ya want. He might be a little cheaper than some other outfitters. I grew up in the house that's used as the bunk-house for the Turkey Creek Ranch.
http://www.heartlandprideoutfitters.com/
Turkeys are thicker than hell here in Nebraska so you shouldn't have too much trouble bagging one on public ground. You can also try asking some landowners to hunt their ground. The worst they can say is no. Good luck and let me know if you have any questions.