I recall the Mamiya 6 had a manual cable release socket on the side of the grip that allowed B usage without draining the batteries, but I'm not totally sure. Check online for the manual to verify this.
VC Bessa R3a & Leica M4-2
Yashica D TLR
Assorted unRF SLR's
Hoping for R4m or GXR-M
For Pete's sake, they're all good. Just get out there and shoot with what you've got!