Cam locks like this?
Just go to your local Home Depot or Lowes and buy standard off the shelf replacement generic cabinet door cam locks.
Search through their stock and pick out the locks which have the same key number. Cheap and effective.
Unless you are hiding valuables like gold, silver or diamonds there is no need for a higher security round lock.
Keep in mind, most of these locks (including the round key) the interior body is nothing more than zinc "IE pot metal" and what isn't pot metal is mild steel so they can be easily defeated with a screw driver or pry bar placed around the hatch..
Since the inside body is pot metal, it tends to corrode easily making the pins or the lock barrel stick from weather exposure over time.
To combat that, a light spritz of spray oil once and a while will reduce the effects of water intrusion. Typically on outdoor locks one would use a dry lubricant like graphite, I found on pot metal locks dry lubricants do not work. My "go to" is a product called TriFlow which is a oil mixed with Teflon..
Spray it right into the key hole and insert key and rotate a few times to spread the oil.
Yes, with the initial spray your key will have some oil on it, you simply wipe off the excess oil off the key and after a few times the key will no longer get oily.