Apparently there was going to be an accessory called "Assassins," likely a boxed set. Item #754.
From a Mayfair ad in the "A Portal to Adventure" book:
"This sourcepack examines the lifestyle of assassins, from the tools of the trade to dealing with the law of the land. This package contains an 80-page sourcebook; a Recipe Book containing dozens of formulas for fantasy poisons; 16 ready-to-sign contracts; a 64-page guidebook that outlines a detailed Assassins Guild; and a full color fold-out map of the Guildhall."
Other than that ad, I can't locate any info that says it was ever made.