I was one of the few lucky ones that was able to get tickets on Ticketmaster after the pre-sale. All tickets are will call, which might explain some of the lack of a secondary market.
In 2017 I contacted BU as an "alum" and was able to purchase from their allotment. Sketchy - Maybe. Regretful - Not even close. I was sitting with families of BU players, which was fantastic, they were a great bunch. Could be worth a desperation shot to contact Michigan.