I assume that the locks are Eurolocks?
You want “keyed alike” lock barrels, but, there’s a bit more to it than that.
Eurolocks come in different sizes - that is how much the part that you put your key into projects out from the door on each side. They also come in different finishes (brass, chrome etc).
There are also types that resist drilling, snapping and ‘bumping’ better than others.
I changed all the locks in our house shortly after when we moved in and went for one key that opens everything. On some doors I wanted thumb-turns on the inside so that they can be opened from inside without a key (for convenience and fire safety).
I ended-up ordering mine from a U.K. company called the handle store:
https://www.handlestore.com/locks/yale- ... o-cylinderThey have some good guides about how to measure your existing locks, and why anti snap and anti bump locks are important.
If you go to places like Leroy Merlin then they’ll sell some packs of keyed-alike cylinders and if you’re lucky then you’ll find something that fits your gate/door. Otherwise it will be a case of having the cylinders made, either from somewhere like the handles store, or by a local locksmith.
If you wnat to buy locally then I’d probably contact somebody like David Beck. He’ll pop around and take a look and probably be able to order what you want. You’ll probably be best to get him to fit them too, as it won’t cost very much if he’s coming around anyway.
Pete.