Here's yer bone! I suspect "American Eagle is a trade name used by some harware chain to name some cheipie single-shot 22. It is NOT a maker's mark. I suspect some outfit like Iver Johnson or Stevens made it back in the day. Can't be worth much.

The Numrich Arms Gun Parts http://www.e-gunparts.com/model.asp?idDept=7outfit might have the part you need. Otherwise, you might have to whittle itwith a file from a block of steel......