Nope, they're still there, Zany. I visited them at Easter and John Leslie couldn't have been more helpful. They're well connected by tube (Kilburn on the Jubilee Line), bus, or North London (Richmond-Stratford) rail link.

But he will probably tell you (as Allodi also say on their website) that repairing old accordions can often cost more than the instrument is worth. (This is the story with many old harps too, so it's not just that someone is trying to sell you a new one.) Best bet is to take it in and get a quote:

2 Loveridge Road (across the street from the tube)
Kilburn
London NW6 2DT

Telephone: 020 7624 9001

Website: http://www.accordionsoflondon.com/