Hi, my name is Melvin! Can anyone suggest a service who could help me with a wheelchair repair?

I hope we can get along and help each other. I have used a powered wheelchair since 1987. I live in North London and love to make use of public transport to get around. My chair is old and obsolete but It’s a good one that works beautifully apart from a flappy castor. I believe it needs new bearings which is not a big job and the parts are standard. As you probably know, once your chair becomes a couple of years out of production, no firm will service it. I’ve currently run out of options for handymen or local friendly garage mechanics to help me out with these sort of jobs. Can anyone suggest a service or person who could help me?
Any suggestions gratefully received.