Believe Compton Abbas may be an option. Check
www.aerobatics.co.uk As for Norhh Weald, I was under the impression that you didn't have to bring your own Yak, but may be wrong on this. Might be worth a call to Alan at the Squadron to check on this: 01992 524510.
PS: overheard in an Essex flying club last year (true)
Yak Driver 1: "You dahn any formation then?"
Yak Driver 2: "Nahh"
Yak Driver 1: "Orright then, you lead and I'll fly up behind yer"
Let's hope they were heading for North Weald to join the course!