They're mostly Japanese sites, but even if you can't read Japanese you can still understand pictures...
360cc Link
This is the largest collection of links to 360cc Kei Jidosha sites I know of and includes sites about Subaru 360, Mazda k360/R360/Carol, Mitsubishi Minica, Suzuki Fronte, etc. Well worth looking at some of these sites (my own 360 site is listed here too)