Where do you source your soil ingredients? (UK)

[astronoob]

Hi,

I want to get some ingredients like:
- Fired clay
- Pumice
- Lava rock
- Pine bark

I know already that clay can be bought cheap as Cat litter.
But the other ingredients seem to be super expensive and hard to find.

So anyway, where do you guys buy in bulk at good prices and good quality?

I've found this pumice for example, I'm not sure if it's a good price and quality:

Pumice 3-8mm – 40L – Indoor Organics

www.indoororganics.co.uk

Thanks in advance