Error in trade

[Plucas1]

hi my problem is that i have two accounts to evolve my pokes between eithers in my main account this i trade a onix to the other and when id like get it back the poke is block and i canot trade him again this onix is from hoenn and this account is in kanto .exist the possiblity to get him back to the original account ? plz help me D;