Surely I cannot expect manufacturers to create new bags for an old Bronica SQ system. 
Yet, I believe I found a a very good one to carry a bulky Bronica SQ-A, with a 150/4.0 + hood, a metered chimney viewfinder, and a 120 back, all mounted together, and still have a little bit of space for a few extra bits: Naneu C700. The bag’s top lid, that has a system to hold it open/vertical for easy access, is particularly convenient for the Bronica, that is notoriously large and not easy to drop in the bag otherwise. I had never heard before of Ex-Pro but I am now positively impressed by its characteristics.