Tried wiki; yes I know it's not always accurate.
It shows 612 as forming at Martlesham Heath (Suffolk) in 1955 and disbanding there in 1963, then re-formng at White Waltham in Dec 1978.
Unusually there is nothing listed for 637 prior to 1966.
Shown on wiki as 'List of Royal Air Force glider units' but there are some errors I have spotted.