In my opinion, if you are going to be hired as a Sheriff deputy you might want to keep in mind that unless you have the same work schedule every week (which I think it will not be the case as a new deputy) you will have hard time finding and keeping clients. Clients have their own busy schedules (not to mention their personal lives) and they usually like to train around the same time each day/week with little flexibility. You’ve mentioned that you will be looking for part time work once you get hired by the Sherriff’s department, but I think it will be difficult to do. I may be wrong, but from personal experience I have to say it will be challenging to maintain any steady clients. Working as a law enforcement officer your life and schedule could become unpredictable and having a second job (especially as a personal trainer) will be tough to do.
As far as looking for ways getting new clients, you will need to devote time for networking. You will need to join networking groups to promote your business and services. You could also place an ad on craigslist. Word of mouth is another way as you already probably know. If you work for someone else (or a gym), this is usually done by them. But if you want to work for yourself you will be responsible to find your own clients. I hope this helps. Best of luck to you at your new career!