The Kanchanaburi Sapphire is found in a province in Thailand called Kanchanaburi. Kanchanaburi Thailand is where the classic movie "Bridge Over The River Kwai" was filmed.
Anyway, they were discovered there in the 1918. Since then however, the quarries have been pretty well depleted of these precious stones. Consequently, the sapphires have become quite rare. Rare to the point where today's miners must now sift through 50 tons of soil just to find one carat of this precious gem!