The cosmetics are available by making any Among Us related purchase on the Epic Games Store between June 9, 2022 and June 9, 2023. According to Epic's FAQ, "This promotion is part of the Epic mega sale, and to get the cosmetics you must make the purchase on the Epic Games Store during the promotional window."
Once the cosmetics are unlocked, however, they will be available for use on all platforms linked to that Epic Games . The back bling puts a crewmate on your back, with all the standard colours available to choose from. It even makes the impostor kill sound when you get a kill! The distraction dance is Fortnite's take on the hand-clapping, foot-stomping animation from Innersloth's game. Epic also notes that "these cosmetics will be available in the Fortnite in-game shop at a later date."
You can check out the collaboration items below:
https://twitter.com/ShiinaBR/status/1534899722347024384
Other recent collaborations include an original Fortnite Chapter 3 Season 3 Battle leans into Lucasfilm with popular characters including Darth Vader and Indiana Jones parachuting into action.