I think that North Weald is keen to include a flight of Chipmunks in the Formation School -but maybe this does not help you either...
The person to contact at North Weald is Anthony Hutton, who runs the Formation School. Alan Couchman at the Squadron will have Anthony's contact details.
As far as I know, the Compton Abbas formation weekends are conducted in Yak 52's and Yak 50's, so that may also not help you too much. Try contacting
[email protected] who is instrumental I think in the Compton formation stuff.