Seems that only 5 T500's were ever built, with Tom Bigelow, Janet Guthrie and Roger McCluskey running one in 1979, and Unser running a Pennzoil liveried car until the Chaparall was finished.
Jerry Sneva drove one in in 1980:
http://www.canamcarsltd.com/car/1979-Lola-T500-HU5-IndyCar...