Looking for parts source for 1988 Flxible

[VictoryRacingCamp]

I am director of a youth camp in Portland.  We bought a 1988 Flxible bus from the Portland bus company a few years ago.  I am now looking for a parts source.  Fortunately, I don't need much right now, but its good to plan ahead, no?  What I am looking for now is a front right turn signal lense to replace the one someone backed into while it was parked over the winter.

Any help would be appreciated!