Replacement keys for Macbook keyboard

So I've learned since I came on the discussion forums today that apparently you aren't supposed to pop the keys on a MacBook up, even to clean under them, which seems awfully impractical to me, and is also too late for me because I have already done this. A couple of times, in fact, with nothing bad happening, but this most recent time, somehow I lost one of the two wire scissor mechanisms under the spacebar. That was just the start of it; with the added stress on the remaining mechanism, the two outermost tiny clips holding the key to it broke off, so now it slides out of place every few words, depending on the angle of the laptop. I also lost both of the little curved plastic things that sit under the keys, for the left command key, and now it won't pop back into place at all.

I've found a place online to buy replacement keys, but they're just the key and the mechanism, not the bits underneath. Does anyone know if these things are necessary, and if so, where to get them without having the whole keyboard replaced? If they're that important, they should be in there a little more securely; I ran canned air under the bottom edges of the rows of letter keys, and had at least three of the plastic things shoot out from under keys that were very definitely still in place.