Missing Key

Keyboard has about 100spare ones!
Joking aside can you be more descriptive on your problem like what hardware are we talking about here.

if you mean a laptop key

then you can buy single keys off ebay etc

if its a laptop is it just the key part with the letter on it or the whole thing including the little scissor mechanism?

if its just the key the new one just clicks on if its all of it then its a pain to put back on