Uh, OK.
Actually for the amount of work involved.....
You can import AU vehicles fairly reasonably sometimes.
...and I bet the movie car was simply cut out and never intended to have actual glass inserts and seals.
...and also wasn't required to survive any longer than the movie production schedule (or the final battle scene).
Also, they are rare but 1973-77 "colonnade" body gms had t tops as an available option.
A 73-74 cutlass might work for you.