your best bet:
www.onlinemazdaparts.com
however before you buy a new one you might be able to solve the problem yourself....pop it off and look at the magnetic pickup to see if there is any kind of metal shavings or anything on it....that can throw off the reading since it is kindof a sensitive sensor
if after that you still have problems then replace it, if you have a buddy with a protege then just swap it with him first to see if it solves the issue...usually your best bet before buying any part if your buddy is willing