Andosol soils can occur where ever volcanoes exist. There is nothing "magical" about akadama, or kanuma. It is possible to find similar deposits through out the world. The Japanese deposits have been mined for centuries, and a few of the oldest individual mines are close to being depleted. There are plenty more locations in Japan, they won't run out entirely, but prices of akadama & kanuma will likely rise in the future as the cost of opening a new mine, versus expanding an existing mine will definitely be higher. Cost of opening a mine in the USA is pretty high too. Think the equipment needed to run a gravel quarry, plus the need to purchase the land the quarry will be sited upon.
Most of the cost of Akadama for non-Japanese users is transportation. It was cost that kept me from using it as I initially got into raising bonsai. I will be interested when SAkadama becomes available through Superfly (who is a member in good standing here) and Bjorn Bjornholm begin to make the product available. And any other USA or Canadian vendors who begin representing the product.
Turface and Monto clay are not similar to Akadama or Kanuma. Turface and Monto clays have significantly higher calcium contents. They are not equivalent.
I am glad
@Sakadama has been posting, it is allowing us to consider a new product. When I get a chance to try some when I repot this spring, I will let people know my opinions and results. Right now, I am open to the idea of another growing media alternative.
In the near 50 years I have been growing bonsai, the single most revolutionary component that improved my growing was pumice. Once I discovered affordable sources of pumice, my bonsai improved dramatically. The second most radical improvement was the realization that a sieve, to sift your bonsai media was essential, and vastly improved the quality of any mix. Sorted to a uniform particle size, almost any material could be made useful for growing bonsai.
Akadama has certainly given me good results. Akadama-pumice blend is my current go to mix. I will be interested to try out SAkadama as it becomes available.