I was wrong. There are actually a whole bunch of Sandy Koufax sketch cards in the 2011 Topps Series 2 boxes, and they are starting to show up on eBay. I've captured them below for you to enjoy. On top of that, a Series 1 sketch card of Jackie Robinson is also on eBay.
This one is really nicely done. It is a drawing of Sandy's 1965 Topps card, and is drawn by Brian Kong.
Here is a Koufax fashioned after his 1955 Topps card.
Here is the Jackie Robinson card fashioned after his 1952 Topps card that was found in a series 1 pack. It was drawn by Kevin Graham.