Where I can find free stock footage of the old-fashioned 5,4,3,2,1 rotating countdown in black and white?

Answer 1

What you are referring to is the old "SMPTE" time code countdown (btw, there is no "1"). You can buy it once and use it over and over. This may have changed over the years and it might be available free now, but in the past you had to buy it to use it legally.

SMPTE = Society of Motion Picture and Television Engineers.