It's not necessarily built in to the class, but thieves are kind of known for being manipulators. Think social engineering, con-men, etc. So one approach might have been to con the information out of people. Ask other thieves. Failing that, ask non-thieves. Failing that, offer to pay people for the info.

You can also search for them using the item search at our official site:

http://www.carrionfields.net/itemsearch/?item_type=weapon&slot=any&material=any&weapon=mace&damtype=any&min_avg=&keywords=blackjack&area=&affect=any&flags=&align=any&sb=level&so=desc