I would imagine the Japanese influence to be quite strong in the 1950s, as they had pretty much annexed the country in the late 19th Century. Rural buildings seem to be heavily thatched, with quite simple mud walls in some areas, while others have less substantial wooden slatted or panelled ones.
More urban buildings share a lot of common features with pretty much anywhere else in the temperate zones of the Far-East, with brick buildings (rendered or bare) mixed up concrete ones and a mix of flat and gabled roofs. Tiles and corrugated iron seem to be the commonest roofing materials.
It's going to be a case of making your own I think... 'Samurai' buildings are likely to be too archaic or too 'Japanese' I would imagine. Having said that, some of Jim B's buildings, with thatched roofs, would work for me. Some of the square or rectangular thatched 'Dark Ages' buildings out there, might fit the bill too.
