What did the vitamin B12 do to you that justifies having him killed? I would start by asking around the shooting ranges in seomyeon and haeundae. Even hitmen need to practice every now and then.
You can get a vitamin B12 injection at any general hospitals where the gastrointestinal specialists are available.
If you would like to have an injection here at Dongeui Medical Center, please call me at 010-9457-8941 to schedule a visit.