I would recommend doing one of the following:
Buy 14mm pegs, and make a tubular spacer to fit between the axle slot in the peg and the axle. I've done this with an old 14mm Primo Stogie, a cut down 10mm-14mm axle spacer and a 10mm (3/8") Vandero axle before, and it worked fine while I was learning predator grinds.
Or you could buy 3/8" pegs, and drill them smoothly with a 9/16" bit. Don't use a 1/2" bit, because it will be too close for comfort, and you'll end up filing away the inside anyway. I've also done this with a separate pair of Primo Stogies, and it worked fine. If you do this method, be sure to buy carbide bits.