One thing about colleges is they always have bulletin boards galore. Try making fliers to put on their ad boards, and check them at least once a week. If you happen to know anybody that goes to a college you can use that person to hand out your ads. One way that I have seen to advertise is to make your ads with little tabs with your contact info
on them, this way they can tear the tab off and you can keep count of how many tabs have been removed.