Note: you do not need to own the game on GOG, PlayStation or Xbox to get this DLC. For Epic and Steam platform you need to own the game to claim. DLC is free until January 31st, 2024.
Epic (game needed):
https://store.epicgames.com/en-US/p/warhammer-40000-rogue-trader--limited-outfit-pack
GOG (game not needed):
https://www.gog.com/en/game/warhammer_40000_rogue_trader_limited_outfit. Add to cart and gift it to your own email. Gift is valid until year 2199, so you can redeem the gift at a later moment if/when you own the game.
Playstation (game not needed):
EU: https://store.playstation.com/en-gb/product/EP6646-PPSA15678_00-0708989918382477
NA: https://store.playstation.com/en-us/product/UP6646-PPSA15692_00-0708989918382477
if you have problems using above links, try this regional free search link (first result): https://store.playstation.com/search/warhammer%2040%20000%20rogue%20trader%20limited%20outfit
Steam (game needed):
https://store.steampowered.com/app/2696650/Warhammer_40000_Rogue_Trader__Limited_Outfit/
Xbox (game not needed):
https://www.xbox.com/en-us/games/store/warhammer-40-000-rogue-trader-limited-outfit/9mzp51bps04m