There are a few ways to approach this:
-You can list it on a various sites (for example Craigslist, local newspaper, community newsletter, etc.).
-Contact other fitness professionals in your area to see is if anyone is interested (IDEA fitness site is one way as you have already done).
-Contact a brokerage agency that specializes in selling businesses. They work on commission, but they have the ability to contact a lot more people and/or other businesses that are looking for investing opportunities around your area and also around the country.
I hope this helps. Good luck to you!