That should not be too difficult because health clubs are forever on the search for instructors. However, you need to be prepared to offer a variety of formats so that you are of greater value to a club.
If I were you, I would just call around. You will be, in all probability, a part-time employee without any benefits. You may also initially only be used as a substitute unless they have an open slot that needs a permanent instructor.
But even if they no not need somebody right now, I am sure clubs will like to know that you are available and will get back with you when they have an opening.