I don't know of any repository of S&W catalogs in PDF. However something almost as good are old editions of Gun Digest and the Shooter's Bible. I think the publishers of Gun Digest offer CDs of the full run of Gun Digest back to 1944 at a fairly reasonable price. Each has a catalog section for every maker, not just S&W. Old editions of Shooter's Bibles are where you find them. I have some going back into the mid-1950s.