The only series one I’ve been slightly familiar with (not mine) many years ago didn’t have locks that I can remember.
It’s not a marque I’m clued up on to be honest.
Ask your question here https://www.lrsoc.com/forum/index.php. You are more likely to get a sensible reply . I do know they are available but can’t give you a company name at the moment .
If you are asking if an aftermarket option is available then there are a few ideas floating about at the moment. A few later series owners fit garage door bolts as extra security.
Sadly they will require visible alterations to the vehicle that may bother some.
Cheap enough and reasonably secure but I’m afraid I don’t know if the Series 1 door will accommodate them.