Origin of Armenian Cataphracts?

[Raygereio]

But when? where? what they look like in the beginning of EB timeframe? I'm trying to find some sources and battle records......

Don't know if it's of any help; but I remember having read somewhere that Armenian Cataphracts were persent at the Battle of Mesopotamia (war between Armenia & Parthia - 88 to 85 BC).
For the life of me I can't remember where I've read that though; but knowing the man's habit of stuffing his wall-of-text posts with all kinds of nifty historical details, I'm willing to bet it was in one of The Persian Cataphract's (what's in a name?) posts.