Hi There,
Welcome to the Forum!
There is something wrong with your identification. Your Grand
Father's revolver looks to be a S&W .38 DA Second Model (based
on the cylinder and trigger guard). The Fourth Model serial num-
ber range is 322701 to 539000. What is the serial number?
As to parts, there are a few places that have some parts for
these old DA's. You can contact Jack First Gun Parts and/or
Lee's Gun Parts. Make sure you have correctly identified the
model type before ordering parts. Also, there may be some
hand fitting required (sometimes).
Cheers!
Webb