I found $1 deck boxes that work perfect for Keyforge cards with sleeves! : r/KeyforgeGame
KeyForge: Accessories - KeyForge: Gemini Deck Box - Blue - Tower of Games
KeyForge: Aries Deck Box - Blue w/ Faction Sticker Set | Premium Parts Place
Keyforge Deck Box for Sleeved/unsleeved Card Sliding Lid | Etsy
Burger Tokens op Twitter: "One of our customers made an incredible excel spreadsheet to generate these awesome inserts designed for our Keyforge deck boxes. Read more about it and get a link
KeyForge: Aries Deck Box - Red | Board Games | Miniature Market