Apple refusing to repair

Apple repairs are all or nothing with very few exceptions except when it involves some of the free repair programs.

If you have a 2017 or earlier MBAir, then you can find replacement key caps and scissor mechanisms online. However, beware that most Apple laptops have at least two variations of the key cap & scissor mechanism so you want to make sure to get the correct one for your particular laptop. Make sure the vendor you are purchasing from has very clear information about how to identify which key cap/scissor mechanism you need.

Get the machine returned and seek out an independent repair centre.

That said liquid damage may very we have introduced corrosion across various caps. The diagnostic will have found them.

I did a Google search and the are numerous sources for replacement keys. However, being the

U.S., Google presented me with U.S. sources.

Try doing a search where you live for replacement keys.