I think the problem might be an ammo box drop glitch.
No, the bug is simple to do. Maybe the mod is outdated since some servers dont allow you to do that.
1.Bind a button with "kill" or "explode".
2.Be BLU.
3. Make sure round has ended and a new round has yet to start.
4.Touch the resupply locker. When the red medic arms appears, press the button with the bind that makes you explode or kill yourself. (When you die, you MUST not instantly respawn or it will not work. So wait for the results to appear since instant respawn will be disabled.)
5.Wait for a new round to start.
6.Touch the locker
7.You got all three medic weapons!
Note: On death, you lose your Medigun and the Syringe Gun