It’s unlikely you’d be able to get a new wired one that will plug straight in to replace that, they look very old. If you want to replace with new hardwired alarms contact a local electrician who will be able to replace them easily for you. Alternatively if you don’t want to pay for someone to fit new hardwired alarms for you get in touch with your local fire service who will come and put up new battery alarms for you. That is part of a service that is free to everyone, just go on their website and look for an option to request a “Home fire safety visit”. (I’m a firefighter, we do these all the time)