Robin, many gyms will specifically request that that candidates possess NCCA accredited credentials.
I think it might be a good idea to approach it from the perspective of what are the credentials your prospective employer wants you to possess. Once you meet that requisite then, I believe, you will be in a better position to choose what gyms might be a potential place to work at.
I wish you success.
I see you are a fitness instructor now and are probably looking to be a personal trainer. Thus I assume that you are teaching group exercise classes in one or more gyms. If this be true, you can ask in one of those places whether they are looking to hire a trainer.
Most gyms have a certain degree of trainer turnover and are always looking to hire. I would inquire in the one gym you like the best and have the best rapport with your group exercise participants because they may be your first clients.
As far as looking outside the gym for clients: do not forget that you need to get your own liability insurance in that case. When you train as a trainer at a gym, that is not necesarry because you will be covered under the insurance policy of the gym.