Welcome! Cute little car
If you would like to buy a replacement sail window(s), Paul McKibbon is highly recommended. fierosails.com Otherwise I'm sure someone has some kicking around.
If you still have your board, it can be recovered in fabric or vinyl pretty easily. Even if it's cracked or broken, it can be fibreglassed to strengthen it back to normal. They're pretty flimsy after all these years.
Gary