Yes and no. The Stinger S34 is a Tokyo Marui M3 shorty clone. You can source stuff like vertical grips for the pump. Or different stocks for it. But they're generally rare and expensive.
Best to do is just paint it up nice and leave it at that. This isn't call of duty, use your sights.
Magazines/shells can be found pretty easily up here, there are some pretty prominent retailers here that supply them. Explore the forum more before posting, it'll save you a bit of guff from some of the users here. Generally its best if you help yourself first, than ask to be spoonfed.
The searchbar on the top of the site will be VERY helpful. Even if you think its a dumb question, type it in and chances are you'll find it already in discussion.