I'd second the Black Hills of SD. Lots of birds and more land than you'll be able to hunt in the entire season. Even I've been able to shoot a few there. I'll be heading there in another two weeks after I finish my season here in MN.

You could also hunt the Black Hills unit in WY. Lots of guys also do pretty good in the Pineridge unit in NE. Although I've never done it personally.

These Merriams are a different bird than the easterns. Try to hunt them the same and you'll go home empty handed more times than not. It's a running and gunning game to cover as much ground as possible. Don't hunt sign because these birds cover so much ground that if you're not working birds(even if there's sign everywhere)they aren't there anymore. Come back later on though because they will likely return.

Good Luck!