My first thought when you posted 311 A was that the gun is a Savage, as I have the Fox/BSE - the cousin of the 311.
If the trigger guard isn't that expensive, you buy it and try it - if it doesn't work, selling it on ebay might work - but if the gun was made by Savage, I suspect it would fit. They weren't going to make TOO many modifications for a rebranded price point gun, which is what Sears was after.
If you haven't looked at Proofhouse, here's the link. Maybe there is another number on your gun that corresponds to one of these to give you the right match:
http://proofhouse.com/cm/house_brand.htm