You can buy replacement screws from Smith & Wesson (1-800-331-0852 in the USA). I think that they only sell stainless screws now, but you could call and ask. If you want blued screws, there are probably places that have them.
They have different part numbers and different prices for the screws to fit different stocks, so the screws are not the same.
Here's the link(see below) to the parts/price list. Select your revolver from the list on the left then look at the parts list on the right. Stock screws are number 43.
I think they can send you the screws in a stamped envelope, so shipping is no biggie. You may want to order several screws to make it worth the trouble. In fact, if you only need one screw, you might mention the revolver's Model Number and type of stocks and someone here may just send you the appropriate screw.
http://www.smith-wesson.com/wcsstore...ist_Retail.pdf