I reckon there a more Soul collectors in Newton Aycliffe, Mark, than in Japan.
First I came across was late 70's (Hitoshi Ishaguru) who bought loads of Southern and deep things from me at the time.
The Japanese collectors, I've encountered, have a healthy obsession with Southern and indie / modern stuff, but I don't think they've anything like the number of 'fans' as we have in the UK... it's just that the ones that are out there are every bit as obsessive, or more so.
Remember being beaten to a Record sale, one Sunday morning in California, by three Japanese guys. Felt sure they must have stripped all the Fame & Goldwax off the shelves before I got there.
Was relieved to find they were into Kiss & Queen and had never heard of James Carr... or Spencer Wiggins!