Get an HP comparitor. They are much easier to find and do the same thing. Douglas just reproduced the reference cards for them.
I saw a bugtrap on an ops bench years ago. I have not been able to find one, even on ebay.
Actually not as crazy as it sounds. Get a known tested working good Williams CPU. Populate 23 of the RAM positions with known good RAM, change the last RAM position to a ZIF socket and you have a 4116 RAM tester.