Does anyone know of any out there?
A simple enough project, but one that is sort of useful, is to use your own income/expenditure information to produce the sort of information that you (or your accountant) will require to work out your taxes.
That's one of the projects I have used anyway. I first wrote mine in BASIC, then in COBOL, and my latest in a mixture of C and SQL.
There are some COBOL resources at the Internet Archive: https://archive.org/search.php?query=cobol
Not sure if they have actual COBOL application code though.
You might also find interesting stuff at Bitsavers: https://www.google.com/search?q=bitsavers.org
Best of luck!