I know of one in my region that goes in and removes the smoke smell when a fire was in a portion of the home. It does work pretty good.
I would practice more indepth house cleaning with industrial cleaners, do more ventilation of fresh air into the house. Even consider using industrial scented furnace filters. Replace the carpets and especially the pads. Go over the entire home and air out everything that can be aired.
This could cost you a fortune to track down and treat this odor phantom. And you may never find it.