Go to
this site and download the PDF under the button "Wheels (by size)" and you can look through most any wheel ever made, both it's size and it's weight. Looks like they don't have any entries for 13" wheels less than 5" wide, that's the VX size, and probably what your wheels are now.
As for 14" wheels there are Miata donuts. They're 14x4" and weigh 9.8 lbs each with the tire. I'm not sure what kind of tires you can find for those, but I'm sure the big obstacle will be finding a tire with a suitably high speed rating. For that I'd try to find antique car tires. They should have all sorts of funny tall/skinny sizes and (relatively) high speed ratings compared to donut spares.