Thru-The-Wall Air Conditioner Installation

We need to replace a Thru-The-Wall Air Conditioner in our brownstone. The unit is encased in an old, make shift sleeve and it appears the bottom of the unit has been plastered to the wall. As such, replacement will be more tricky than simply pulling out the old unit and sliding in a new one. Does anyone know of an air conditioning specialist or mason who can provide an on-site estimate of the work and cost required to replace the sleeve and air conditioner (and repair the wall if necessary)?