hello Paul,
there are many websites that offer buttons and whole mechanisms for keyboards. I have already mentioned many of them myself (my sons and roblox :-) you know what I mean). The cost is small, a few dollars. Replacing them is quite easy, basically a small flat screwdriver or a small teaspoon is enough. Using Google, I found over 100 working sites that dealt with a similar problem. Take a picture and send it by e-mail - someone will answer.
* regards,