Try to get your hands on a financial report for Cabela's. On the assumption they are a publically traded company, there will be an annual report. It would be fair to guess that half their revenues are related to selling hunting products. Of course, there are other hunting product stores out there, noteably Bass Pro Shops. Bass Pro Shops may have revenues 60% fishing 40% hunting, just as a wild guess.
You may be able to get information on-line from states that show the numbers of non-resident hunters for different species. Try looking up Colorado non-resident elk hunting numbers. Do a quick calculation of money provided for big game licenses. At $350/license for non-resident elk and up (I'm just ball-parking it here, y'all) you can come up with a rough figure of what one state takes in for one big game species. This is just a taste, and a full-up analysis is more complicated. Colorado is the biggest elk hunting state, so their numbers are not representative of all states. Different species, different states have different licensing fees and numbers of licenses issued.
Hunters spend money on gas, food, lodging, and entertainment as they go on out-of-state hunts. How much? That may be difficult to estimate. Maybe call some chambers of commerce and ask them what they estimate the economic impact of hunting is? Try Durango Colorado, Pagosa Springs Colorado, Gillette Wyoming.
All of this involves your following up on these leads to do your own research, but the information should be available mostly on line. How much time before your paper is due? It's getting close to the end of the semester, isn't it?