Excuse me, is there any reliable way for apprentices to recruit fitness instructors?

Reliable, nothing to worry about, you can still get paid if you don't pay. We have it in the gym. In fact, it is a method of recruiting coaches in disguise. Nowadays, good coaches can't stay in ordinary gymnasiums, which are divided into full-time coaches and itinerant coaches, so some apprentices are invited to learn the job at hand while doing it. Have you ever seen a barber shop looking for a barber? Many of them started as assistants, but most of them washed their hair first and learned slowly.