A nice idea for a challenge. Fairly easy for for me, as I although I live in Surrey it's next to the border with Hampshire (and fairly close to Berkshire too) so I regularly go to events outside my county. All that was left was to wait for the Sussex Mid-week Event to turn up at my end of the county and I was done.
Here are my qualifying events:
Surrey GC1Y2C2 Surrey Mid-Week Meet - The First! (attended 8-Oct-2009)
Hampshire GC2C5EQ The Twentieth Monthly Hampshire Cachers Meet (attended 11-Aug-2010)
Berkshire GC2XN7M Monthly Mid-Week Bash in Berkshire #6 (attended 6-Jul-2011)
Sussex GC4A83P Monthly Mid-Week Meet in Sussex #63 (attended 19-Jun-2013)
More details here.
Emma found this one so that makes the score now 2-1-1. I'd already looked there in fact but hadn't spotted it (I was looking for something larger).
I didn't understand the clue at all. Then we got back in the car and Bobcat said - Hang on! Its X isn't it - and of course he was right.