Hi, and welcome to the AC forums Jdroid.
It depends what you mean by "an android". A phone? Tablet? Media Player? TV? Washing Machine? There are Android enabled devices in each of these categories. If it's a TV like one from http://www.peopleoflava.com/ then the cost of the screen will be VERY expensive.
Spare parts for most of these (especially phones) are available either directly from the manufacturers or by specialist sellers. I know of a couple of online stores in the UK that sell phone parts for some Android phones, for example.
You will need specialist tools, and experience in taking apart such devices would be preferable. If you've taken apart a few laptops in the past or a few recent mobile phones, and you have the correct tools (usually very small torx screwdrivers, often ones that work with security pinned screws), then you'll be fine. If you don't have these, bear in mind that these can be quite expensive, and many places will not sell security screwdrivers to the general public, and it will probably be cheaper to take it to a repair specialist, or even better still send it to the manufacturer (give them a call, most manufactures have a repair service).
If you haven't done stuff like this before, and don't have the tools, then trust me - leave it to the experts.
