KAT, the part # for the nut is 8-97229-212-0. Get four new ones and they'll be a perfect match for $30-35 total. Does Tim's in Prescott or Power in Scottsdale still carry Isuzu parts? Check 'em out. They may have 'em in stock. If not, it's the same exact nut as a Honda Passport. Give the Honda parts guy that number and his system will instantly convert it to the Honda number and see if it's in stock.
It's also the same nut on an Axiom, Rodeo, Trooper, and Amigo. If you stop by a junk yard they should have dozens of 'em.
Mark