You can catch the full series, including this arc, on major streaming platforms like Crunchyroll.
After Gintoki, Katsura, and Kondo are mysteriously turned into cats, they find themselves caught in a war between a gang of stray cats and the "Cyborg Cat" army led by Hoichi. In this episode: Gintama Episode 191
: If you're a new viewer, don't skip the first two episodes of the series; while they are technically filler, they introduce the chaotic energy you'll see in full force here in Episode 191. You can catch the full series, including this