Hi, OliviaPresland!
Thanks for reaching out to Microsoft Community and posting your inquiry regarding your Surface Laptop 3's key.
I am afraid to inform you that there are no spare parts for the keys. When the Surface needs to be sent in for service, a replacement is provided for an exchange of the unit.
If you opt for key replacements, you can check online if there are any available.
Kindly check with a Microsoft Surface Advocate for assistance. Please visit this page https://support.microsoft.com/contactus/ to contact Microsoft Support. If you are outside the US, you can check this https://support.microsoft.com/help/4051701/ page that has the Global Customer service phone numbers for Microsoft.
If this answers your question, please let our Community know by marking this post as an answer. Otherwise, don't hesitate to respond to this thread if there’s anything else that needs to be addressed.
Kind regards,
Janette_Z