Is it now impossible to buy lodgings via the alternative payments that the opportunity cards used to provide? (I have 15 antique mysteries looking lonely on my shelf)
I think so, unfortunately =/
Not at all! The Brass Embassy lodging can be got on the Hell faction opportunity card, the Bethlehem Hotel one from A Merry Gentleman (shows up ubiquitously at Nightmares 5), and the Bazaar Premises can be obtained in the Bazaar Sidestreets, from the offices of Baseborn and Fowlingpiece.
It is possible but you have to get the right card, for the Royal Beth you need to see the Merry Gentleman and for the Brass Emabassy you need to see the Devils, or got to the right place, the Bazzar Sidestreet for premises at the Bazaar
Also, FYI, it’s 50 antique mysteries required for a Room at the Beth, not 15.