Annabel what a brilliant idea of yours, to organise an Au-Pair "Meet".
back in the '70s I used to live in NW London and there was a small Disco (oops showing my age) that advertised specific nights that Au-Pairs were welcome to enter free ( with a free drink included) - It was always well attended and the Au-Pairs made lasting friends.
Of course it was a magnet for young men as well (I wonder why) ... of which I was one (*blush* ahhh the memories!). A very canny move on the Disco's owners parts for what was an otherwise unremarkable venue.
Surely some enterprising Wandsworth coffee-bar or bar owner can advertise an Au-pairs evening (on NVN naturally) and sit back and wait for the money to roll in!
There you are bar owners , I'm laying gold at your feet for you to just pick up!