Hi Bethan, I'm not arriving until the 27th but may have the same problem, I read on Bourricot Express website that if you spot people on your plane or at the airport that need transport to St Jean you can text the names and number of people to Caroline of Bourricot Express and that allows her to pick them up from the Airport too. Check the details on the website, but for the service they offer you should have plenty of takers, it will save Pilgrims having to make the way there by train and bus over a protracted number of hours.
The next update of the Bourricot Express travel manifest on there website is the 16th, so you might get some last minute names added, keep you eyes glued on the website come the 16th.
Good luck with the search and Buen Camino.