At this time the only means to replace the keyboard is to replace the assembly it is part of. Review this IFIXIT guide: [guide|44898|Retina MacBook 2015 Upper Case Assembly Replacement]. As you can see its a bit of work as you'll need to take the entire system apart. Here is the part you'll need: [product|IF301-001|MacBook 12" Retina (Early 2015) Upper Case with Keyboard - Used] that IFIXIT store has available.