Dishdude: Chevron has quart coolant bottles, but I'm not sure if they are 50/50. I believe Exxon/Mobil is also Texaco, and Texaco has Dexcool in quarts also, but again I don't know if it is 50/50. Try a Chevron station
Tomcat27: If Dexcool eats some gaskets (which it does), Flushin and putting in new Dexcool shouldn't stop it from eating the gasket. I believe the gasket problem is only with some V6 GM engines. The new V-8 Voertex does not have any coolant near the intake gaskets.