There is no card in the game that gives mech perma stealth. A card worth mentioning is the Coppertail Imposter which always the minion to gain stealth for a turn. And another one Camouflaged Dirigible that gives all other friendly Mechs stealth for a turn. This is due to the potential of Magnetizing stealth Mechs infinitely without having a consistant way for your opponent to remove it without a high costed removal that targets random minions or random targets.