Razmuz,
The M547 is pretty scarce. S&W produced approx 10,240. Published production dates are 1980-1985, however due to problems the first units, beginning with s/n 6D, were not shipped until 1983 and ended in 1984. The 3" are RB while the 4" are SB. You can find them on the auction boards from time to time bringing $750 and up.
Good luck in your hunt.
Jim