I "performance drive" on tracks like Road Atlanta.  Where can I get upgrade rotors and pads to improve my brakes' stopping power?

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Literally everywhere.

EBC Yellowstuff pads are a good street/track pad. You should also change your brake fluid to a performance fluid such as Motul 600.
A good addition is the Brake Bias Spring which puts more rear brake into your Corvette. Several places offer this, one is Doug Rippie Motorsports.
Also consider changing the rubber brake hose lines to steel brake lines.
Another option is the C4 Stainless Steel Caliper Pistons. The stock caliper pistons are aluminum which transfers heat to the pads and fluid more quickly than stainless steel. Again Doug Rippie Motorsports has these.
No matter which brake set up you wind up with another good addition is Brake Cooling Ducts.  Corvettemods has the chin spoiler ducts and hose kit and Lambert Automotive has the C4 Duct Plate Kit.

Take a look at Vette Brakes and Products, https://www.vbandp.com