Seems most any autoparts store has them. Napa didn't have the lever or spring for the ebrake, and it seems none of them come with those anymore. I was lucky to find one caliper with a new lever, but that was all they had. You might have some luck in another part of the country if someone still had them in stock. GM discontinued the part so the dealers can't even get it. I was lucky to find some in the wrecking yard so I can use the levers from them. They are ~$100 each for a loaded caliper. You can also buy some from BlackWidow performance brand new for $300/set.
The wrecking yard is your best bet for the levers.