factory a/c car heater core replacement, where to purchase new core

factory a/c car heater core replacement, where to purchase new core

hello everyone still trudging along on the 71 demon, have the hvac system torn down for repairs and resto, having a problem finding a replacement heater core for a factory a/c equipped car, found the evaporator but every place i have searched only has a core for one without air any help on this......thanks michael