Where can I find a replacement for a keyboard key?
Unfortunately, in almost all situations it's necessary to replace the keyboard since most manufacturers do not have single keys available for purchase. However, in the case of a laptop many companies do offer keyboard key kits, which contain many of the parts necessary to fix their keyboards.
Swap keyboard keys
If the manufacturer does not have replacement keys or any kits available and there is a keyboard key that you don't frequently use such as the Windows key or menu key consider swapping it. You can remove any key that is the same size. For example if your H key was sticking or lost you could place the Windows menu key in its place.
Contact local repair shops or ebay
Local computer repair shops often replace and fix keyboards on laptops. It's possible that they may have spare broken keyboards that they'd be willing to let you have or use for spare keys.
Additionally, many keyboards and other spare parts are sold on e-bay and other auction sites, check these pages for replacements.
Notice: If this is a laptop key, keycap, or key component make sure you're getting a key or keyboard that is compatible with your model of laptop. There are dozens of different laptop keyboards and they are not all compatible with each other.
Sticker worn keys
If you need to replace a key because it's worn out consider purchasing a keyboard sticker set instead of replacing the key. These are available in most computer retail stores and online stores.