You can get a replacement by writing down the bitting that you've found and take it to a locksmith who deals with tubular locks and code cutting. If you give them the make of that lock (or the vehicle/equipment it came from) The locksmith will be able to identify the correct keyblank and cut the key to the bitting you give them.
If for some reason the customer has the "code" from the key and gives it to you, you can go to a locksmith and simply give them the code, tell them what the key is for, and they should be able to cut it directly from that as well. It's really much simpler than you think.
Of course, the other option is to purchase a tubular key duplicator, and insert your tool on one side, blank on the other, and duplicate it straight from your pick.
