The Stevens 311 is not too difficult to disassemble and fix. For a good guide to complete disassembly look here:
http://marauder.homestead.com/Stevens311.html . If you find the worn broken part, try Numrich at this URL:
http://www.gunpartscorp.com/Default.aspx.
A drill bit works well for the drift pin that you will need and a variety of sizes of regular blade screwdrivers is almost a must. Use the right size, you'll regret it and the scratched up screws if you don't.