If you want Merriam's, your going to have to go to NW Nebraska. The public land is easy to find on the NE public land atlas. The rest of central and SW Nebraska is indicated as Hybrids. SW used to be shown as Rios, but the maps were adjust a few years back.
If you are going to KS, you'll need to be in the western half of the state to be in Rios. I think north and west of Salina is a pretty good description of what is considered Rios. KS puts out a map of the subspecies distribution. Look at the KS WIHA. Use google earth to verify the WIHA has timber and go from there.