Quite a few 1917s are available, more of the Brazilian contract revolvers. The 1950 and 1955 models are a bit more scarce.
Once you get into the numbered series, there are quite a few.
You have to search and be patient but you should be able to find them.
BTW, there is no 25 no dash. The 1955 evolved into the Model 25-2 right from the start. Not sure why this happened but it never followed in the series of dashes that other N frames did.
Which model are you looking for?