IMO, you will generally have the best chance of getting the correct parts if you call a Chevrolet dealer that specializes in Chevrolet trucks. Most likely they will not be the cheapest in town but you have your best chance of getting the correct part numbers. (and the correct parts) After all its only your suspension. You can usually buy OEM parts at a discount online if you search. Have your VIN handy. Ball joints don't normally fail so be careful. There are other aftermarket manufacturers that make better than OEM parts but all can be lost if they aren't correct for your vehicle or they are installed incorrectly.
Chum lee