Hi
At the moment I can’t find any listings for the keys them selfs but I can find donor keyboards you can get keys from however they are pricey
https://www.ebay.co.uk/itm/314587326371?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=puiheshhspy&sssrc=2349624&ssuid=0ACG7idPSQ6&var=&widget_ver=artemis&media=COPY
It might be worth a trip to the Apple Store as they might be able to replace individual keys at a slightly more reasonable price
Hopefully this helps
Any questions please ask
Thanks:-)