What they said is correct, I'm not sure it warrants further explanation but might aswell,
just for fun!
As mentioned by HolmgårdViking, the Corinthian helmet fell out of use and was succeeded by Chalcidian and Attic type of helmets and the former would fall out of use roughly a century later if I recall correctly as the Greeks were shifting increasingly towards easier to produce and more open-faced helmets types. I remember a book mentioning the Spartans adopting the pylos type of helmet over the Corinthian one as a message that they didn't hide themselves behind a helmet (Was it history of the Greek helmets ?).
The most recent (in chronology) Corinthian helmet I ever managed to find after some extensive research was dated ~400 B.C. and dug up from a Scythian grave and it was most likely a trophy because it seems highly unpractical for mounted combat.
Now the Italian factions/tribes/colonies might have the closest resembling helmets to the Corinthian, the Apulo-Corinthian being a direct evolution of it saw extensive use in Italy and up to the first century A.D. if my memory serves well:
The Etruscans (Rasenna in the mod) used the Corinthian helmet around the 7th to 5th century B.C. so logically they made their own variants and evolutions of the helmet in a sort of italo-chalcidian helmet:
Then there's Megálê Hellás, the Greek colonies in southern Italy that make use of Italo-Chalcidian helmets as well:
The vast majority of helmets in Italy are based on this thesis:
http://discovery.ucl.ac.uk/1348999/
That's as close as you might get to the Corinthian helmet in this mod unless someone comes with rock-solid evidence of the usage of the Corinthian helmet in 300 B.C. and Rgcotl then bothers to model it.
Alternatively this
Open Source Pack includes a Corinthian helmet which you can then add to the mod yourself for your own enjoyment, everybody is happy
Concerning the bronze cuirass, there's a bunch of them in the mod but all "muscled" cuirass as bell type of cuirass:
also fell out of use around the fifth century B.C. if I recall correctly.