Greg:
If you can remove the lock (by dissassembling the pump) you can take it to a locksmith. Otherwise you will have to have the locksmith come to you. Another possibility is to find key 'blanks' that fit the opening and slide into the lock. Buy a few for this project. Start by coloring the edge with a magic marker and sliding the blank into the lock. Wiggle it back and forth like you were trying to unlock the lock. Remove the blank and look where the marker has been removed by the motion. Take a small triangular file and - using one point of the file - start filing down the areas where the marker has been removed. Look at any key you have to see how the cuts are shaped. Only take a little at a time. Re-color the edge and repeat the process. As you progress, some of the 'cuts' will stop having the marker removed as you try the lock. When this happens - quit filing that particular spot. Soonor or later you will get all of the 'teeth' cut in the lock and it should work. You might go through a few blanks trying this, but if you spend your time and don't rush, it will work. The trick is finding the correct 'blanks' to start with.