How about these from Speedzilla? Not a 5", but maybe an option.
SUPERMOTO WHEELS Produced by Carrozzeria specifically for super motard.
Available for Yamaha YZ/WR, Honda CRF, & XR650R
FRONT WHEEL: 3.5" x 17" REAR WHEEL: 4.5" x 17" (5" Rear Available 08/06) WEIGHT: Front wheel = 7.4lb / Rear wheel = 10.8lb COLOR OPTIONS: Black, Gold, or Clear
Front brake rotor can be included at an additional charge. Front brake mount accepts 320mm rotors only. It is the same bolt pattern that Ducati & Aprilia use, which means there are a ton of brake rotor options available.