I have heard that, if you can keep an air tight enough room
and use Co2, that if you can get the concentration of the Co2 high enough]
that the spider mites will just drop right off the leaves

you would need a tank, a regulator, and a hose into the room
i am just passing along what i heard,
i have no practical experience using Co2 to kill mites
however, it will work but only at pretty high concentration

sorry i can't help more
the cold has taken care of all my mite issues