Account bound armor previously purchased from Cartel Market not available

Hey there! After reading what you said, I'm assuming you're trying to unlock the level 31 armor sets like the Outlaw's Armor Set in collections? If so, I'm afraid those level 31 armor sets need to be bought or obtained on each character, regardless if they pop up in collections; as there is no option to recollect them or unlock them for your account. I hope this answers your question!