Carfromjapan.com has the best search features I’ve found, once you know what you’re looking for https://www.goo-net-exchange.com/ is also nice because they translate the car condition sheets.

Parts availability depends on the car. For the Rasheen for example most of the engine parts can be found at any parts store for the 1500 and 2000 cc engine versions cause those engines were also in American cars. I’ve also found English websites that are easy to order just about any parts you want for a Rasheen including body panels.

Once you find something that interests you just Google that car name parts and you can usually find someone talking online about how owning that car has been for them.