Wally, look for a custom box builder.
They can make any size you want
You may want to call a contractor and see how much it would be to modify your garage door header instead.
or even build a new separate garage if you have the room on your lot.
least that way your WIFE won't have to scrape snow/ice off her car and leave the kid's bikes outside while your part time POS truck takes up all the room in the garage!!!
LOOZER!
..L.T.A.