While Viz Media has tackled the more recent material with Osomatsu-san, Discotek Media dipped into one of the previous anime series last year with Osomatsu-kun.
Crunchyroll has made it completely binge-worthy as they’ve added the complete eighty-six episode run in one drop rather than doling out big batches every week or two.
Done up with English subtitles, availability for it is set to unrestricted, so you can sample it below.