Bathroom vent cover size on a 1979 Southwind

[underscore]

I'm trying to find a replacement vent cover for a 1979 Class A Southwind.

The standard sizes I see out there are 14x14.  However, mine measures 13x13.  Am I just measuring something wrong and a 14x14 will work?  Like, the cover is 13x13, but the vent is 14x14?  Or should I be looking for something else?  I can't find any reference to a 13x13 vent cover

 

[Tom]

You could try one of the RV parts or salvage dealers here.