Saw on the Retro Rides site there's a monthly meeting at the AV8 café at Cotswold Airport/Kemble airfield, every third Sunday morning of the month so next is 21st July.
I went along last Sunday just for a look and it's a fantastic site, plenty of large commercial jets parked up plus a Hawker Hunter and Red Arrows Gnat at the café, also an ex RAF Bristol Britannia being conserved that you can get aboard. Worth a visit anytime.
The entrance to the café is from the north side of the airport off the A433 Tetbury to Cirencester road.
Hope to see some GT4's there.