I went to the Sherborne Classic Car Show in Somerset in July (not sure why our club doesn't attend as it is a massive event with loads of clubs).
Simply the club is run by volunteers, no one person in the club has a calendar or diary of every car show, autojumble, Land Rover event.
It is down to the local areas to decide if they want to attend an event.
Possible event attendance are maybe brought up at the pub meetings and if there is interest in an event the local area organiser will help, if bookings are needed or co-ordinate some sort of club stand/display.
Often, there is no great interest as maybe there's another equally popular event somewhere else.
I've been to shows where I'm the only club "representative". We have leaflets, cards and membership forms (though this can be done online in the field now
).
The area rep has access to club banners and signage etc.
If someone thinks there's a show or a classic car run going on - mention it to other local members and see if there's any interest in attending.