I use both Isuzu parts suppliers they have both been good and I have had no issues with either one. Just check price and availability for your area, there prices vary buy a little but you still get Isuzu parts at a good price, but may have to wait for back ordered items to come from Japan so think ahead and wait for it.
http://www.isuzupartscenter.com/
http://www.isuzuparts.com/

I even found some good deals still on parts that are still sitting on shelf at the local ex-Isuzu dealerships around town, it never hurts to call them and see it they have any extra Isuzu parts laying around that they want to sell. I scored a brand new still in the box front bumper cladding for $500.