WTB 1973 Dart Front Signal/parking lite Sockets

Looks like a NAPA Echlin LS6477 should do the trick, but compare the focal length carefully (how high or low the bulb sits in the socket); it may also be an LS6478 or an LS6458. You have to get the focal length right or the lamp won't distribute the right amounts of light through the needed angle ranges.

(Or you could forget the sockets entirely, remove the lenses and reflectors, shave 1/8" off the grille bar where it enters the park/turn lamp space, and neatly epoxy in a pair of these excellent and inexpensive LED units that just happen to be perfectly sized).