Dell does not sell keys, I'm sure its too late for you, but might help others. I bought some laptop keys for my Dell Studio 15 at individualkeys.com, they are great, fast and cheap.
Hey I had the same problem a couple of months back and I was about to order a new replacement keyboard but one of my friend suggested me for "www.laptopkey.com" and I ordered my replacement keys from them and saved a whole lot of money. They have a great customer service. I will strongly recommend this to you. They also have understandable video installation guides to help us fixing our keys. You can check them out.
You can now buy individual replacement laptop keys, you do not need to buy a new keyboard, here is a great site that sells laptop keys, good luck.