Hi MikeSpock!
Thanks for reaching Microsoft Community. We're here to help and let's work on this together.
Regarding your query, unfortunately Microsoft does not offer any replacement for single key damaged on type cover. The type cover as a whole needs to be replaced already. I understand that buying a new type cover is not in your best interest but feel free to check on Microsoft Store Microsoft Surface PCs, Computers, Laptops, 2-in-1s, Dual-Screen & All-in-Ones | Microsoft Surface online for Surface Go type cover anytime.
Thanks again for choosing Microsoft! Hope this helps!
Regards,
RodelioP.