Hi,check out http://screwfix.com they sell just about anything.
I would also check your local stores they will give you advice.
Good Luck

Sure you can replace the lock without replacing the whole door. Should be able to pick one up at the hardware store,or your nearest home improvement store

I’ve yet to see one that you couldn’t replace just the lock, although it may involve the entire handle assembly.

Home depot etc all diy stores carry handle/lock sets for sliding glass doors…The trick to this is take in the old lock to get the proper one..they are pretty universal except the way they latch..very easy to do
here are some examples..but no need to order online..all major diy stores handle these

I’m sure you can replace the lock assembly only. I suggest you go to your local hardware store or better yet any home improvement store such as Lowes, Home Depot etc and speak to one of the people in the proper department. They are usually quite knowledgeable and can be helpful in getting your problem solved. Tip…. I suggest that if possible you take a couple close up pictures of the lock assembly from different angles to show them as there are many different makes and styles. They should be impressed with you for bringing pictures. Better yet see if you can remove the lock assembly and take it with you if possible. Also knowing the manufacturer of the door will help.

you could just replace the lock.