I don't like having to have different keys for different locks. A few years ago I found a Box of locks at Lowe's that were all keyed alike. Never seen that before. Yes I've seen packages of 4 keyed alike but never the entire box of locks with the same numbered keys. So I bought a number, more thsan I figured I would need. Well, I want or need two more with the same key.
So I browsed the Master Lock website. I discovered it is possible to order locks to fit keys you have as long as you know the key number. Fill out an online form and someone emails back within a couple days and you get a quote. They said about a 10 - 14 day turn around. Pretty good price with a 15% off they offered for buying within 7 days of the quote. Shipping is additional but there is no need for another and different key. They can also do a "master" keying with different "sub-keying".
I bought a dozen of the round masters all keyed the same from my favorite Do It Best Store / lumber yard. I know most people can never use that many but with a ranch and storage units down in the valley............
What I saying is you can special order larger lots also.