I have a selection of windows from a mid 70's import camper. The dimensions are as follows :
Small vent windows - sold
Medium slide window 18 1/2" x 31 1/2" - $30
Small slide window 13" x 30 1/2" - $20
Large slide window 16 1/2" x 41" - $40
Front window 12 3/4" x 59 1/2" - $40
Small fixed window 20" x 16 1/2"