Would an MTB flat mount caliper mate up with a BL-M785 lever? If so best place to buy said Shimano caliper?
Yes, they'll work together.
From looking arond they're like hens teeth so good luck getting hold of one!
Hijack: do cable calipers exist for flat mount?
Hijack: do cable calipers exist for flat mount?
Yes
TRP and Tektro do some for starters
Would an MTB flat mount caliper mate up with a BL-M785 lever? If so best place to buy said Shimano caliper?
Madison (uk distributor) are out of stock of all flat mount mtb calipers. SLX due in June, XT in December, no due date for XTR. They only do rears as well.
Is there a converter from post mounted caliper to flat mount?
Yes - Shimano and Aztec do adaptors for PM callipers on FM mounts.
It's mad at the moment with regards parts. Picked up some flat mount Spyres, still trying to find some bolts to attach them to the frame!
Good luck with your search
Shigura may work? They do a flat mount caliper.
Bump: Workaround time....would Sram Rival PM caliper work with other brands adapter, Aztec or Shimano PM to FM?
Yes