I am pretty sure there is no such thing for Sora, because Sora has an internal reach adjustment.
http://www.bikeradar.com/forum/viewtopic.php?p=14721525
Specialized makes shims for 105 and Ultegra.
http://www.specialized.com/us/en/bc/...jsp?spid=41915
You might be able to trim them to work as well, or you can use Sticky Back Foam. I have heard it works just as well as the actual shims