Bicycle Research still makes them.
http://www.bicycleresearchtools.com/access.html and Bike Tools Etc.
http://www.biketoolsetc.com/index.cg...rts&sc=Spacers stocks them.
They were more often used to trim the freewheel position and usually go by the term "freewheel spacers."
You may want to check the following before proceeding: 1. do you have more than 2mm of threads exposed on the adjustable cup (left side) beyond the lock ring; 2. is there more than 2mm clearance between you crank and the chainstay on the left side.
As a point of reference, triple bottom brackets were usually 5 mm wider (all on the drive side) than those designed for doubles. That's why you want to double check your non-drive side clearances before proceeding along this path.