Hello Jay,
Peter Best? - believe they may only have a sub 20 year concession for MGs.
Could also try:-
Lancaster, Haggerty, Carole Nash, Heritage, Gotte & Wynne, RH; etc. Also, any insurers linked to this forum?
Some 'everyday' car insurers will also consider doing an additional 'classic' vehicle as an add on you your policy, particular if you have owner-driver (just policy holder covered) on the basis that you can only drive one car at a time!
Only other suggestion is to try the performance VW websites and forums and magazines, since some of these cars may come under the sub 20year old category.
Good luck with it, and thanks for being able to update this forum - always useful.
Kind regards,
Gareth.