Caps lock key falling off

The actual key caps themselves can be replaced referencing my answer in this previous similar question (the mechanism for the key switches in this model and the one in the post are the same). The Caps lock should be a similar process, but there may be some additional hooks. Double check the back of the key cap to make sure none of the plastic latches are damaged. One of these days I will get around to writing a guide on this.

If you need to replace the actual keyboard, that’s a bit trickier. You may be able to find the keyboard as a standalone part floating around the internet. But those standalone keyboard replacements are a real bugger since Apple has them riveted into the top case. If you decide its worth it to replace the whole top case, they can be found in the iFixit store, as the top case including the battery or without the battery installed.