Well 1 way to open it would be have pop items drop off of all enemys in the area that pop the NMs which gear drop from. That way everyone can fight the NMs and get gear still like with the Arch-NMs for Dyna. Perfectly honest I have no idea though because I never really did Salvage, always seemed more annoying than it was worth to me, so this might fit nothing of what Salvage is/was and could be completely stupid nonsense.