https://na.alienwarearena.com/ucf/show/2168846/boards/contest-and-giveaways-global/Giveaway/warframe-excalibur-avalon-bundle-giveaway

Requires you to create an alienware account to claim a key and redeemed at https://www.warframe.com/promocode.

There were ~4000 keys remaining when I claimed, the Karak and Skana both come with a potato installed, or just sell them for the free weapon slots if you've already mastered them.