I'm planning on pursuing my Grand Slam as well.

Here are the places that I am planning on trying:

Rios: Black Kettle WMA, Packsaddle WMA, or Ellis County WMA- Oklahoma
Merriams: Black Hills National Grasslands - South Dakota
Osceola: Fish Creek WMA, Richloam WMA, Three Lakes WMA, Green Swamp WMA or get an outfitter

I live in LA, so I don't need to travel for Easterns as well.