Fragrant woods, namely agarwood or aloeswood, that are used for kodo in Japan are getting very scarce. The price of kyara and jinko seem to rise yearly. I read somewhere that only ten years ago, top grade kyara could be had for 2500 yen a gram, about 1/8th of what it is today!
Scarcity of wood didn't start recently. When Japan was under feudal rule during the Edo Period, the country was closed to most foreign countries. If I remember correctly, Japan traded only on a limited scale with Holland, Portugal and China. (I might be wrong about Portugal...) Since all fragrant materials including aloeswood had to be brought in from abroad, the supply was very limited. Also it was during the Edo Period that kodo became very popular among the princesses and came to be considered a part of proper upbringing. Since supply of wood was very limited, only a small amount could be burnt at a time. The word that is used to describe the amount of of the precious wood used in kodo is "babi-bunsoku," meaning literally, as thin as horse's hair and small as a mosquito's leg.
This kind of expression and sensitivity to material seems very Japanese to me. Since Japan never had much natural resources of its own, its citizens had to always rely on imports and also be very thrifty about materials. Words like "mottainai" meaning "precious, not wasting, holding off" all at the same time are unknown in English as far as I know. In that sense babi-bunsoku could have only been born in Japan, and kodo is a thoroughly Japanese pass time.