If a vapor barrier was not used during construction of a house under stone, brick and dryvette siding, is there anything after the fact that can be done that would serve the same purpose?

Some brands of paint offer a variation of a vapor barrier. Consider Moisture Vapor Barrier However, this would only serve to keep your insulation from getting damp from moisture within the home. You may need a masonary sealer if tere was no tar paper under your brick. Who did this installation anyway?