Brake light switch for your '64 is still an off-the-shelf part from any auto parts store. Standard #SLS-147 or NAPA Echlin SL-778. The rear terminal is a 1/4" spade instead of the round bullet/barrel type used originally through '65, so you'll need to install a female 1/4" spade on the end of the wire. Very easy. Re-use your original switch bracket; use big pliers to crunch and remove the original switch from it; the new switch comes with a retainer sleeve. Adjust the switch so it turns the brake lights off reliably no matter how quickly or gently you let off the brake pedal, but do not try to use the switch as the up-stop for the pedal, or you'll beat the new switch to death in a hurry.