It's not quite in Lincoln, but not too far I don't think. Quail Run Horse Centre in Elkhorn Nebraska. I rode with Jim Urban back in the 80's and he was a fabulous instructor then. Looks like he is still going strong and his sons (who weren't even born when I rode with him) look great in the saddle. Try the website at quailrunhorsecentre.com
Check out www.nebraskadressage.org. Their newsletters have boarding advertisers, which may help you get started. A friend of mine in Lincoln - her parents have a farm - I think they lease the property to a dressage trainer, but I am not sure if that is correct. I'll check on it and send you a pm if that is the case.
My new mantra - \"Life is too short not to eat ice cream.\"