There were similar M&P snubbies made prior to and during WWII, but in limited quantities. As there were only small numbers made, those early M&P snubbies are therefore very collectible. Many more were manufactured during the postwar period as yours was. The S series M&P snubbies are somewhat more plentiful than the earlier versions, but are still desirable. Unfortunately, yours is in far from high condition and does not have original grips. It is probably worth in the approximate $400- $500 range at most, as it is only in "Shooter" condition. Regarding ammunition, any .38 Special you can find will be satisfactory. Regarding original and period correct grips, they are available, but are not nearly as plentiful as they were not so long ago. A high condition correct pair will probably run in the $100-150 range today. Not sure I would bother looking for a pair as the cosmetic condition of your snubby does not warrant the cost. The correct grip design was used during the 1940s into the earlier 1950s, and is called the "Sharp Shoulder" design. But any K-frame grips, new or old, will fit. Check eBay.