Interstellar Operations Universal Technology Advancement table should answer to a lot of questions.
Generally speaking, unless otherwise specified, tech spreads to other factions within five years of one faction debuting production version.
Eg the Free Worlds League debuts the Longinus in '57, it includes advanced armor. Should be available to everyone circa '62, even if no one makes use of it.
Capellans have advanced armor in 74 at the latest with Fa Shih "Support".
Mimetic armor, the Cappies got the tech in '65 through unknown means. Few factions ever make use of it though, off-hand only the Republic and Free Worlds League have used it beyond Cappies and WoB. The Taranis and Ogre Interdictor have it.
EDIT The issue isn't the usefulness but the slot requirements, few suits can make use of it, and most factions favor medium-sized designs that have a lot of issues with Mimetic armor.
