I'm sure there is a ebullition or old fashioned board at all the colleges you are interested in advertising to. Usually it's in the cafeteria. Give them a ring and ask them where you can post such a thing. Best of Luck!!
First make sure you check with your local laws/regs to make sure you are able to lease out rooms and that you meet the requirements legally. If you have already done so, advertising on sites can be tricky, in particular this site is designed to connect agents to buyers/sellers and agents to agents, I am not sure this may be the best site to look for the assistance you are seeking but possibly going to the help bar on that site may help you find the answer you are looking for.
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