I just bought some of the 12x12" cork boards from one of the home supply stores, they come in packs. I have built several army display boards, tall ones, using "pulled' cork.
NOT pulled PORK!
If you have the patience, and it sounds like you do, they turn out very well for rocky formations, hills, mountains, unit and army bases, etc.
Go for it! Put up some pictures when you get done!