They can also be picked up at a cooperator.
From Ranger station: For all other reservations, the forest asks visitors to plan to pick up permits in-person. Permits can be picked up at a Forest Service district office or a cooperator. For a full list of cooperators, visit the link below
Be sure to confirm hours of operation and location when choosing a cooperator.
I sent a message to Maggie at the Kawishiwi station to see what Virtual permit groups need to show for a cooperator to issue the permit.
BWCA permit cooperators