Look at this site
McMaster-Carr part number 2162K14 is an 18 inch long Hose that screws into a modern grease gun and has the correct female coupler to mate to the alemite grease fittings.
Part number 1089K11 gets the brass male grease fitting.
The only place that I know of that has the cap is Restoration Supply Company
RSC. The Part number is LUB091
Hope this helps.
Ken GASCH