Chad and Djibouti have already been mentioned. The latter works both before and after independence. The adversary can be a communist Ethiopia or an irredentist Somalia.
Madagascar claims the Glorieuses (also claimed by the Seychelles and Comoros), Bassas da India, Europa, and Juan de Nova. It was a leftist dictatorship between 1975 and 1992, and that would be the best opportunity to invade, but AFAIK there's nothing in those islands to be worth the bother for them.
The Comoros claim Mayotte, which is worth the bother, but they're not going to put up much of a fight. None of the other Indian Ocean claims produce anything.
War with Syria over Lebanon is a possibility, except I think Syria would have already provoked the Israelis before the French.
Suriname claims part of French Guiana, but not an important enough part to make an impression.
France supported the Front for the Liberation of the Enclave of Cabinda. If these guys managed to take power during the Angolan Civil War and hold it long enough to grant the French some major oil contracts, they might end up intervening against an MPLA attempt to retake Cabinda.
Finally, Vanuatu was very opposed to French nuclear testing and supportive of New Caledonian independence under Walter Lini, but you need to push those tensions pretty far to get actual war.