Hi. The simple answer to "How many surviverd ?" is Hundreds !
As a Paramedic in B'ham I've covered the greater B'ham area from Marston Green to Solihull to Woodgate to Handsworth to Sutton to Castrle Brom, and can tell you that many Anderson Shelters are still in use as Sheds, and even Garages ! Many Municipal ones remain, some hidden, others there but sealed off. Some, like the one near me, (Its still Top Secret), were modified in the 50's & 70's to house Local Gov't in the event of a Nuclear Strike by the Eastern Bloc countries.
My Grandfather, a Driveway & Small Builders business owner, was barred from Service in WW II as he was deaf, but used his Lorry and staff for Heavy Rescue in the Sutton/Erdington areas after Bombing Raids. He also had a number of Anderson Shelter Corrugated Sheets in his back garden up until his death in the late 70's. These were the remaining stock from his 'Phoney War' period of constructing these for people. My Uncle in Walmley has a brick built Shelter in the rear garden, now a shed.
Also, dotted across the margins of the Urban fringe are the Pillar Boxes to guard Road Junctions and Manufacturing areas.
The old City Shelters had mixed fortunes. Some became Underground shops in the City, others were demolished. One, in Handsworth I think, and another in Lee Bank, were destroyed in Air Raids, (surely someone will know about these ?)