Rod,
You are shooting a traditional bow, not a rifle, so your shots are going to be at most 40-50 yards so you don't need mountains, just 10 to 30 feet of elevation depending on the slope you are trying to simulate. Try shooting from a treestand set high and go for targets that are 20- 40 yards away. Another method of simulating the slope will be to shoot from the top of a small hill at targets set on the hillside or at the bottom of the hill; you can also go to the bottom and shoot up. There is always a way to do it, just be creative.