Yeah, I think I own the only M.Suzuki, FW-518M in New Zealnd. I am fairly sure about this, as it was a sales reps sample that did not sell, so I bought it at his imported cost and have owned it since 1976. I can't find any info on it at all.
Like your's it seems to be getting better with age and Ive heard that accoustics don't generally do this, as they tend to soak up moisture.
It has a heavilly inlaid vine pattern on the kneck and is very well made with no age related delamination whatsover even though I do not keep it cased and its taken some severe knocking around at times.
I have never seen or heard of another one anywhere but would love to hear from anyone who knows anything about it. It has the usual Martin Drednought appearance and big fat sound.