Following the assasination of Marjoran, the Western Roman Empire fell apart rapidly. Aegidius, the Magister Militum per Gallias, refused to acknowledge the Emperors after Marjoran and set up a state in Gaul north of the Loire. After the death of Aegidius in 464 or 465 CE the Franks under Childeric may have taken over much of the army although this is unclear, but quite plausible given the pattern of Frankish expansion of the areas they controlled in the following years.
Sygarius the son of Aegidius held on to some territory around Soissons until his defeat by Clovis in 486 CE. However, it is highly unlikely that this constitued some sort of successor Roman state as was orginally suggested decades ago before more in depth research indicated that this was improbable. Other army lists which allow this are somewhat behind the time (by decades). In reality he was just another "post Roman" warlord, one amongst many and not the strongest.
By this stage, any "Roman" troops would have been mostly recruited from barbarians and the majority of the army would likely have been recruited from Franks and be tribal in nature.
Using Gallic Foederate Roman in MeG
Armorican allies - Armorican and Early Breton (only from 468 to 470 CE)
Saxon allies - Old Saxon (only in Gaul in 468 CE)
Frankish allies - Early Franks (before 485 CE)
Gallic Foederate Roman as allies
Gallic Foederate Roman is not available as an ally for any other list.
Troops and suitable miniatures
Example Army Lists
10,000 point Maximus list created by Nik Gaukroger