Hi Melodie Unfortunately, there is nothing I can think of to uniformly seal a masonry wall. You certainly must have a double brick layer with a small air space in between. What is most likely happening is air is infiltrating around brick mortar, going into the interbrick air space and them finding small openings into your living space.
Odd though it may seem, the best thing you can do to reduce (you will probably never eliminate) inward cold airflow is to make sure your attic is fully insulated from the living space below, and that ALL openings from below are sealed. Warm air naturally rises, and if there are small openings into the attic space (such as holes for wires and ducts, plumbing pipes, etc), this warm air will rise into the attic, creating a vacuum in your house living spaces, which will draw in outside air from wherever it can be found....like around old mortar joints. Other sources of air leaving your house include a furnace that draws combustion air from inside the house and then vents the burned air up the chimney (same for gas water heaters), fireplace chimney flues and poorly fitting windows and doors.
Unfortunately, air-tightness was not a priority in the 1920's.......and to get that, we have to put a lot of work into making our older homes as tight as we can.