You can also check the availability of pass reservations in France on the Belgian railways website.

Note on the side: many USAers tend to think they are and have to use that specific train-in actual fact there are most often dozens of alternatives-other times, other outings, perhaps with a change more. IN France only these superfast TGV trains MUST be reserved-but on domestic routes hese often run every hour or so. So if your wanted 9.55 is full (highly unlikely though) take the 8.55 or 10.55!