Edit: Not a real series. There’s just the one story in Watchmen and an adaptation of that.
Tales of the Black Freighter is a swashbuckler anthology pirate comic book series. It was published by National Comics (which later became DC Comics).
Shying away from mainstream adventures, Tales of the Black Freighter’s radical and innovative stories show a disturbing reality against metaphysical terrors and perverse comments on the human condition.
As I’ve mentioned in my other comment, I think the way this wiki describes the in-universe lore has mislead you. It wasn’t a real comic series, it only exists in Watchmen. Moore came up with the history of the comic companies in the Watchmen universe because he thought it wouldn’t make sense to have comics about superheroes when superheroes were real.
Ah, thanks for the correction. It did sound like there was an actual series given the dates and mentions of DC Comics etc. Well, at least there is Marooned and the adaptation.