The original Black Widow skin from the Fortnite x Marvel Avengers Set was last seen over 1,500 days ago. The skin dropped in April of 2019, and within a month the skin was gone. All Marvel crossovers always look great in Fortnite, but the Black Widow skin looked particularly badass. There were two styles: one with her short red hair from The Avengers, and one with her more recent blonde hair for the Avengers: Endgame release.
Epic Games did release a new Black Widow skin in 2020 as part of a crossover with the film, Black Widow, but the skin is not anywhere near as nice. In fact, despite the red hair and spy-outfit, the skin does not resemble Natasha Romanov at all.
Epic Games routinely brings Marvel skins back into the shop at random times, but with Scarlett Johansson’s exit from the Marvel franchise, it is unlikely fans will ever have a chance to get the Black Widow skin again.