I know there was a shortage of the clay type in the UK in 2010/11.
The trouble is, you can't just use any clay.
I am speaking broadly here about clay used for horticulture, and specifically about those used for expanded pellets.
The most commonly used/available commercial clay in the UK is broadly split into 3 groups. Bentonitic, Kaolinitic and Illitic.
The type we need to make Hydroton is Kaolinite (with a little illite). It's formed from weathered rocks from millenia ago when England was tropical.
It's also used in it's raw form in huge amounts at many county-class cricket grounds. (Trade-name Kaloam).
2/3 years ago, the company that mined and processed it in the UK (cant remember the name but they were a sports aggregates company and the guy responsible went bankrupt). A fault in a processing machine resulted in gravel in the clay and many of our world-respected highest-quality cricket squares were badly damaged, mostly the top teams.
There was as ensuing chase for the last of the clean Kaloam clay in the country and the company director declared insolvent and vanished only to reappear running another company doing the exact same thing.
British cricket will suffer for years and the guy got off scott free.
Kaolinite's mining and manufacture have now been resumed by another company.
I don't know if this affected hydroton or if it's imported (not financially viable for cricket).