Don't know if this helps but according to wik, the 2.5L was known as the Iron Duke. You're right, finding parts for it may be hard searching for the engine itself, but it has a car list that this engine was placed in. May be able to find a forum or something. And if the Pontiacs you were talking about, Bad99Olds, were the Sunbird, Fiero, and Astre, then you're on the right track.
http://en.wikipedia.org/wiki/Buick_Century
http://en.wikipedia.org/wiki/GM_Iron...engine#Tech_IV