Living in Old Town I immediately thought of:
The Spice House (http://www.thespicehouse.com) for truffles (they grind up their own truffles fresh for their truffle salt... truly amazing)
and Old Town Oil (http://www.oldtownoil.com) next door for truffle oil
...as GenkiTango said - it's easy to make yourself. By the way - highly recommend these shops for all sorts of yum.
1512 N Wells St, Chicago, IL 60610
Old Town Oil
1520 N Wells St, Chicago, IL 60610
Anywhere else? I think they sell it at a pretty expensive price at Whole Food ( I know I know it is truffle butter). I try looking at costco and fresh farm but no luck. I actually see something call truffle something near the butter and cheese section at costco but it is not call butter