Here's a website that has what seems like pretty good information, including photos. Doesn't show anything Giamatti used in 1990 but it does show Giamatti in 1989.
I guess it's possible that the Padres could have had some leftovers from 89 but it seems odd that they would be using them in late July.
Interesting reading anyway, good luck on your search!
http://photos.bigleaguebaseballs.com...LL-010.JPG.php