You can buy the webbing online in the color of your choice. You should be able able to get the hardware from any junkyard.
Buy heavy duty nylon thread and a leather palm, and hand sewing needles from Sailrite. Or go to a shoe repair shop or saddle repair/Leather work/tent or upholstery store to and have them sew in the ends and buckle.
Of course you can buy an extender for each seatbelt. That adds a foot or.more to the buckle side which can make the belt considerably more comfortable (for me) because the belt goes between "the girls" rather than smashing one! I know, TMI.
Today is a gift, that's why they call it the present.