Castrol in UK offer a "Classic" series of lube products; specifically I need the water pump grease for an antique car. Is there a known source in the USA?
May not work but try talking to a parts department at a BMW dealership. They generally use Castrol products. Perhaps their distributor can get a hold of some for you.
Find a irrigation dealer. Centrifugal pumps still use a grease cup to lube rope packings. We are using marine grease for a positive displacement pump for the fire service