Okay I found a place with a good selection of shoes for both men and women.
In men's sizes they stock from 47 up to 54. If you walk along Sonnenstrasse from
Sendlinger Tor to
Karlsplatz Stachus on the right hand side of the street, you will come to a Schlecker's chemist, which has a passageway next to it. Go down this a little way and it is on the right, you can't miss it. It is called something like "Ubergrosse Schuhs". The staff are very attentive, insisting that I actually needed 47s, that I must try both shoes and not just the right and making some commment about the shape of my feet that I did not quite fully catch.