Carleton is (mostly) right, although you CAN convert them if you really wanted to, hunting down/buying the parts is probably more expensive than just selling them and buying some brezza's/aura's
3T made the Mistrals to be a low stack bar (due to an "outcry" at the time that all their other bars had very high stack) and while parts of them (the pad position) are very adjustable, pretty much everything else is not adjustable, particularly stack.
What you have is this
[top]
pad bolts
pads
hardware mounting bolts (for extensions below basebar)
basebar
mounting hardware / extensions
[bottom]
First a caution... DO NOT add spacers BELOW the base bar. The Mistrals are not designed for that.
So your choices with what you have right now are limited to basically adding spacers between the pads and the base bar (I've done this for athletes in the past on this bar so it will work) OR buying additional hardware.
THIS specifically is what you need. (conveniently out of stock) but you could also use any of the mounting brackets cannibalized off of a Brezza/Aura bar. With those brackets, the extensions AND the pads mount above the bar (like the picture I posted above) - if you do this you do lose the adjustability of moving the pads as far out as you'd (possibly) like.
If you look at the 3T AURA bar, it is exactly the same as the Mistral with the exception that it already has this mounting hardware. (and it doesn't have the little holes in the basebar for wider mounting of the pads)