Jarno, acouple of dates to ponder over:
Tunerfest Brands Hatch, Sunday 24 June? The RX-8 OC will have a stand and a large presence, plus club exclusive track sessions too. Clive took his race car out on track there last year. The day usually hosts a "Time Attack" round too, in which PeteH plans to compete in his Eurospec RX-8, with which he was very successful in 2017.
Here's a link to the RX-8 OC topic to give you some idea of the event in 2017. I've not been able to get to the event since the club started going 2 years ago, but it's in my diary for 2018 https://www.rx8ownersclub.co.uk/forum/viewtopic.php?f=18&t=72803
Another event to think about is this one on 25/26 August. It's a static event held at Dunsfold, the "Top Gear" track. You might be able to tie this in with Lydden? https://www.wingsandwheels.net/
It's a static event, but the RX-8 OC will have a stand for there for both days (camping options have been mentioned). I wen there about 3 years ago and it's a HUGE show with loads of interesting stuff for all the family.
Not sure if I'll get to the latter event though, as it's Gwyn's birthday on 25th Aug, but maybe try to arrange a long weekend in the area and combine it.....
Both events are in the South East with loads of castles to visit. Dover Castle is well worth a visit as is Bodiam Castle (pic below). Gwyn and I went to both in 2016, basing ourselves in Rye on the coast for a week, a beautiful town with old cobbled streets (also pictured).