You can get gap bridging fixings for this kind of job but 2" sounds a bit much for then.
I'd suggest a resin fixed stud approach with a tube spacer inserted over the stud to bridge the gap between the brick and the front of the plasterboard.
Like this (fixed width font):
PB Gap X Brick X | | x X | | X X Nut BB| | X X ___||BB| | Sleeve ||X X |___||BB=================||X Studding in resin X \\| ||BB\\\\\\\\\\\\\\\\\||\\\\\\\\\\\\\\\\\\\\\\\ X \\|___||BB\\\\\\\\\\\\\\\\\||\\\\\\\\\\\\\\\\\\\\\\\ X |___||BB=================||X X ||BB| | ||X X BB| | Washer X X BB| | X X BB| | X X Bracket BB| | X X BB| | X X | | X X | | X X
You want M8 or so on the studding so you'll prob need to open up the holes on the bracket.
Actually, you may get away with using a long and beefy frame fixing, again with a reinforcing tube on the outside to bridge the gap. Any slop will tighten up when the tubes go into compression. Careful length selection required to get them pinched up just before the bracket touches the PB or pinch up a mm or so clear and caulk the gap.
Except that sod's law says that one or more of the screws hits mortar or otherwise gets misaligned. Presumably the PB is fitted to substantial timber battens?. I would be inclined to see if I could screw a suitable sized bit of 12 mm plywood to the battens either on top of the PB or after cutting out a section of it. Then screw the bracket to the plywood either directly, or perhaps with cavity toggles if it is a giant screen. If the batten spacing isn't suitable (i.e. plywood overhangs unacceptably to one side) then cut out a "window" in the PB slightly larger than the bracket footprint, then battens on the wall and 18 mm ply shimmed to be flush with the top of the plasterboard.
Isn't two inches on the large side for dot and dab? Presumably if you could locate the dabs you could use them as the load bearing spacers between a bit of ply and long screws into plugs in the masonry, then screw the bracket to the ply.
I'd assumed the two inches were for rockwool or celotex.
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