To my knowledge, the whole housing is not available, just the lens are repoped. GMC originally riveted the lens to the housing and sold the whole unit as a parking lamp assembly. Some might still be out there NOS (new old stock) but are very hard to find. Most used units are discolored and cracked. Brothers sells the repop lens, amber color is correct for '63 thru '66.
http://www.brotherstrucks.com/prodin...number=PLG66AM