What type? It’s usually significantly easier to teach formation with two of the same type. The process can then be translated to a different type fairly easily.
If you can get hold of a second aircraft of the same type and someone else who wants to learn, try the North Weald Formation School run by the Air Ministry (google). It started off with Yak-52s but they will teach in other types. It usually runs in April and October.
Otherwise, try CRM Aviation at White Waltham who use the T-67. it’s them rather than WLAC who do the formation training.