COB is started by the houses that didnt quota at the end of Fall Rush. Then next semester there is Informal Recruitment which is only done by maybe 3-4 houses at the most (thoses that didnt make quota).
After Fall Rush is done check the OGL to see what possible houses might be COBing. As someone said, it may not be the houses you want. Also check next semesters Informal rush too.
My thing is if you maybe want to check back into rush it's possible that its not too late. Call your Rho Omega and see. I dropped out my first year and although I eventually joined AGD a year later (Love it to death with all my heart and my sisters but, I will be honest and say they definately were not my fave or one of my top choices.But that goes to show you never know what can happen and things can be different once you're on the inside ) I still sometimes wonder what would have happened if I have of stuck around until Bid Day.
Best of Luck and hope that you become a member of a great system!