When were the first TVs put on the store shelves?

In the US in 1939 following their introduction by RCA at the Worlds Fair. These were electronic. A few other countries may have had mechanical TVs on store shelves before that, but the electronic TV based on RCA's design soon replaced them.

Unfortunately with the entry of the US into WW2 TV production ceased in early 1942 and the factories retooled to make military electronics.