Harrington & Richardson was the exclusive importer in the mid '60s and early '70s. They were also offered as a stand alone .380/9mmK and as a dual set, .380 and .22. There was also a 100 Year Commemorative issue (100 years of H&R) released in 1971 - had a gold presentation plate on the left side of receiver and some gold filling in stampings. Here's a couple pics of mine - missing the combo tool - but the bolt face can be turned using a small screw driver - also included was a separate .22 extractor for the rim fire cart. I've not fired mine, it is unfired from factory - proof targets were included and numbered to the barrels. I've included a pic of one of the targets - note the date of test fire.
p.s. the '4' was the H&K model number - it had nothing to do with the number of barrels supplied - the single and dual sets were also the Model 4.