The Parkhurst device was a cubical block of steel, screwed (LH thread) to the receiver just above and behind the magazine cover, There is a T-shaped vertical slot in the front face which accepts a 5-round stripper clip. Just 100 rifles and 100 carbines (in the 287-288K serial range) were modified for the device, which actually worked quite well. The main reason that it was dropped was the fact that the M1903 Springfield (a designed clip loader) was well along in planning/testing, so it was not felt expedient to do much more with the Krag. Nearly all of the arms were scrapped, many (most?) by cutting the receivers in two, so finding one is a needle in haystack scenario.

There MAY have been other chargers, or cartridge packets, associated with the 1983 trials rifles, made in tiny quantities by aspiring promoters, by I do not believe that any others were actually made at SA and issued to troops.

Krag chargers WERE made for the Norwegian Krag, but they were only meant to dump 5 rounds in quickly, by hand - no attachment was applied to the gun.

That is the short answer - hope it helps.