I made mine at http://techshop.ws
Reverse engineering a key from a lock is not that difficult, providing the lock can be disassembled. In order to follow this instructable you will have to have access to the lock itself, which usually means the lock is not locked to begin with. If you're hoping to make a key for a container that is currently locked, you'll have to pick it open first, or research the key making method known as 'key impressioning'.
Step 1: Disassemble the lock
Once the lock has been removed from its housing (door handle, drawer, whatever), there is usually a cover on the top of the lock that holds the pins and springs in place. This cover is often clipped in place and can be removed without damaging anything. In my case, the edges of the pin holes were uncovered, but crimped half-shut and needed to be widened with a drill in order to extract the pins. As you remove the pins, keep them in order front-to-back and keep track of the 'top' and 'bottom' pins. Each pin has a specific shape that allows it to interact with the spring, with the pin above/below it, and/or the key itself, depending on where it is sits in the pin-stack. A helpful tool for keeping things straight is a small piece of paper like a post-it note folded into an accordion shape so that each pin-stack can be laid in its own trough.
Removing the lock core from the sheath is usually a helpful step even if it isn't absolutely necessary. I recommend removal if at all possible (but don't pull it out until you've removed the pins, or they'll shoot everywhere!) Sometimes the pins cannot be removed except by pulling the core. If this is the case, be careful to expose only one stack of pins at a time, or you'll have some sorting to do when all the pins cascade out of the lock.