I'd try and see if I could negotiate the clause off the contract, and if I couldn't, I'd find someplace else.
Luckily, my apartment, which is a mere block from campus, doesn't have a no-firearms policy. Then again, neither does the on-campus dorms*.
I love this town...
*they do require that you keep them in the firearms locker, which was in the basement of the dorms, though. And you have to have a trigger lock on the gun while it's physically on campus. However, I know of at least three people, including one RA (although I only suspect that he did), who ignored that rule...Also, OR law allows people to carry concealed on campus with a permit, but you are likely to be kicked out if caught, which is annoying...