My instructor has started classes/clubs in more than one college - granted, he's no longer a college student - but he started in a PE class, then transferred to the community class/club/school when he was in college himself. Some college programs I've seen have 2 classes - 1 that was a PE class, and 1 that was a community class, open to anyone (some students came straight from the community, some transferred from the PE class); other college programs I've seen only have the school/club/community class. It depends on the college and its needs. Rather than trying to drum up support more or less randomly, talk to the the college about what it takes to start a student club - then your options for advertising will widen, you'll be able to access the gym or other appropriate room at a set time, you'll be drawing from a wider range of potential students, and if you're lucky, the college will pay you to do teach it on top of everything else.
Good luck!