I'll go on a limb and say it doesn't exist.
A few years ago, a bunch of "cards" showed up in Global holders that were actually cutouts from a magazine that were glued to the fronts of '35 Goudey 4-in-1s, then graded by Global as 1938 Goudey proofs. They looked nothing like 1938 Goudeys, and contained a bunch of subjects that were not in the '38 set.
All were listed on eBay as proofs and if I recall, many sold for $100-200, all erroneously labeled by Global. Once in a while, one of them shows up on eBay again, and because they're professionally graded, they still sell.
I can't find the thread on CU that references the Slaughter, but there was a thread here on 54 about them back in 2008, and Slaughter is mentioned. Here it is:
http://www.net54baseball.com/showthr...8+goudey+proof
I'm a big '38 Goudey guy, and when I first saw the cards, I wasn't ready to reject the idea out of hand, til someone came forward with the same magazine that the pictures were cut from.
-Al
ETA this is also the famous "Archive" thread.