Well, the last thing I am, is in the know. But this was a problem last year as well.
Several teams that many thought should have got an entry had their cars, or one of them, if they had two, put on the reserve list. RFH Dome and TVR for starters. This was in favour of a few teams that seemed to have come from no-where, and obviously most of them were French. I think all the reserves got a race in the end, but it was such short notice for some of them that sponsorship and preparation time became real problems.
It makes you wonder as to the wisdom of the ACO's first choice, it doesn't make much sense to invite cars and teams that hardly seemed to exist, never mind be prepared.
Drop them a line, put your car on the reserve list. Don't forget the French accent though.