Here is a thought for you, which worked for me in a different application.
I noticed that when it is cold outside, the outline of the framing shows up on the outside of my laminated 5ver walls (exterior). Condensation clung to the exterior surface faster where no framing members were present. This is because the frames represent additional thermal mass that takes longer to warm. Using this principle, I used a can of aerosol spray cleaner, the type used to clean electronics, cameras, etc., and sprayed my exterior wall to locate a frame member. This spray cleaner quickly cools the surface and causes condensation. Worked like a charm - I could see the outline of the frame member with condensation forming outside the frame member but not on the frame member. Now, I have not tried this on an interior wall but assuming the wall is smooth, results should be similar. The ambient temperature may have to be cool (e.g., early morning) for this to be the most effective.
Good luck,
Phil