To my understanding, Latin doesn't have a dual number at all. The adjectives duo "two" and ambō "both" have some special forms derived from the PIE dual (-ō, -ābus, -ōbus), but are considered irregular rather than part of any real pattern.
However, from an answer to an unrelated question:
By the way, another heterogeneous noun with a similar story behind it is frēnum "rein", pl. frēnī. In this case the Latin masculine plural ending continues what was in PIE terms not a plural at all, but a neuter dual.
This points to another trace of the dual number which I hadn't heard about before.
Are there any other irregularities or fossilized forms in Latin which derive from the dual number in PIE or Proto-Italic?