Thruxton do formation work in 4 Tomahawks once a month, I know this because they generally do it straight over my village, so you could try giving them a call.
I've been lucky and taught by an ex RAF instructor for his own reasons, but it is hard in civvie life to get formation instruction. The chap at Thruxton who teaches formation is an ex RAF and CAA Test Pilot, and certainly can teach you more than you're ever likely to absorb.
G