Does anyone know the turnover rate or availalbe positions yearly for the Master At Arms rating in the Navy?

It changes with promotions and the economy.
When you have times like now for jobs on the civilian side the retention rate is higher than it would be at other times. People will stay in longer so you get a compression at the higher pay grades and that trickles down. You can't give a set number.

according to last week's Navy Times, which had an article about projected manning of all ratings for 2010 and beyond, MA is expected to be Creo 2 and 3 across the board for quite some time to come.. meaning manned at or over strength and promotion rates will slow to a virtual trickle.