How available are jobs for undergraduate in Excercise Science?

Sure, especially if coupled with a Phys Ed teaching credential, fitness instructor certification or even a registered dietician certificates. A master's in Kinesiology is another route after you get you B.S. So just an extra credential will complement your degree and boost your employability.

I would say apply to schools to be a PE teacher.

Consider fitness centers and possibly employment as a physical education teacher, assuming you will be certified by the state department of education. However, most private schools do not require certification for teachers.

Hope this helps!