Dog1:
You can find much information on the Wyoming Department of Wildlife web page. You can identify hunting units and drawing odds at different locations on this web page. I think the map you are referring to is a Bureau of Land Management Map, available from the Wyoming Department of Wildlife. Look towards the end of the Hunting Booklet. Maybe this URL will work for you:
http://gf.state.wy.us/downloads/pdf/06appbooklet/06NR44-52.pdf
You are PROBABLY looking for the Gillette, Reno Junction, Sundance, and Newcastle maps. They cost $6 each.
I can't tell you anything about the numbers of animals available out there. I hunted pronghorn out there in 2004 and wanted to hunt in the Thunderbasin National Grassland but made a deal with a rancher instead so I could have confidence that I wouldn't have my hunt disturbed by large stampedes of hunters on the public ground. I hunted in Unit 23, about 5 miles south of Gillette. There are a lot of pronghorn in Unit 23 around Gillette.
I think my next hunt will be on the Thunderbasin Grassland. I might choose to go later in the season and during the week, in hopes of encountering fewer people.
Yes, you can camp on the Grassland.