Model 45 (Post Office)
This model is a special purpose K-frame Military & Police Model
chambered for the .22 rimfire. It was designed as a training revolver
for police departments and the U.S. Postal Service. This
model was manufactured in limited quantities between 1948 and
1957. In 1963 production abruptly began and ended again. There
were 500 of these revolvers released on a commercial basis, but
they are rarely encountered.
I've been hunting for a Maetba 6 Unica in .357 with a 4" or 6" barrel for a little while now. Nada so far.