It's not the guy at the counter's fault. 1989 was 25 years ago.
If you could find a part number for it, you might get lucky and be able to track one down through the parts network but realistically no dealer is going to stock something like that in 2014. It would be really surprising if you were able to find one. The truth is that no one in their right mind brings a car to a dealer that's been out of warranty for over 20 years so there's no sane reason for them to stock that item.
There used to be a list floating around of parts still available for our cars at the dealer but it's doubtful that bolt would come up.
Best bet is the junkyard, here, Ebay etc.
