As far as I know and I don't know much, there is no such thing as over the counter antelope licenses for bucks. Wyoming has over the counter doe/fawn permits for about $30 and you can get up to four of them in some areas.
In the western states with antelope you can go up on the BLM site and download a public lands map. You can get maps from "publiclands.org"
I also use the Univ of Texas map library
You will need to also download maps from the state fish and game agency on units and then download the draw success tables. For Wyoming in the units with lots of federal lands there is only about a one in three chance of drawing.
Like I say, I don't know much about it but the information will get you started.