almost any online audio shop has them. Or you could go to best buy or somewhere like that but you will pay more.
Axxess ASWC Universal Steering Wheel Control Interface
PAC SWI-PSv1 (swipsv1) Pioneer and Sony Factory Steering Wheel

I put your hu model number into sonicelectronix and it pulled up these two at the bottom for adapters for the steering wheel controls. I've used the pac before on a 02 gp and had great results.