I guess you probably tried asking at the "stealership"...
I'm about to get one really cheap for exactly that reason: it's missing all 4 rubber pads. I was think of cutting then out of a used tire, but I don't plan to use that rack permanently attached to the car like most tend to do.
My other suggestion would be to drop by a Thule/Yakima rack dealer. Maybe they can match something by looking at the remaining 3.
