I searched for "Japan" on the British Pathe newsreel archives and turned up 850 results. There are probably more Japan-related clips filed elsewhere.
A lot of the clips fall into some obvious categories: Manchiria, the war, activities of the imperial household, natural disasters, tragic accidents etc. If you've got time on your hands, I can recommend a browse. The dated narration often adds to the enjoyment. Unfortunately, you'll often have to put up with a short ad before the clip plays which can get a bit wearing after repeated views.
Here are some that caught my eye:
Samurai swords on ice (1940)
Mrs Orr-Ewing, who spent 9 years in Japan, demonstrates the tea ceremony (1960).
Video of the first official telephone call between London and Tokyo. (1935)
Japanese in London, including a clip of the city's only Japanese restaurant at the time. (1968 )
Nothing new about "konkatsu". Clip from the late 40s.
1956 German footage of Japan's world champion chicken sexer
1937 Tuna fishing with "oriental-style" narration.
Interesting name for the plane which set a new speed record in 1937 for the Tokyo-London flight.
British attempt to sell to Japan looks as half-arsed in 1968 as similar efforts do today.