Where Are LPG Vehicles?

This is very tempting! I think LPG is extremely under-rated these days.  I remember when I was still a kid back in USSR some people were modifying their LADA's to drive on LPG.  Then when I came to Japan I saw that all of the taxi's are running on LPG.  It can't be that difficult, but I do not see any info, nor a single private owner convert to LPG. I was always wondering about it, as natural gas is the only natural resource that can be extracted in Japan.

Does anybody know anything on converting cars to LPG in Japan?
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