If you're talking about the sling loop that goes into a slot in the toe of the butt plate, Numrich (gunpartscorpdotcom) should have the carbine rear sling loop. Brownells usually has them but they're out of stock. Finding the machine screw may take some doing. There's several sources of threaded fasteners once you know exactly what you want (Fastenal is one). You might try S&W customer service or parts department. They might be able to scratch something up, but I expect most buttstocks show up at the factory already assembled.
If all else fails, GPC has used complete buttstocks for about $22. You can rob parts as needed.
Someone who's upgraded their buttstock to something sexier/more tacticool might part with their original one for less. You might try a want to buy here.