This is where I got them from.
https://www.bark-uk.co.uk/
I suppose you could use them on slabs. I think they could shift around a bit. I put straw on my slabs and now chicken chippings will adorn the mud pit we have now!
Thanks for link. If I did put some down I would have to box the bottom of my runs in to stop them coming out It’s mainly my run with the new girls in that has become extremely messy. They are poop machines! They are so not clean and tidy like the polish. I’m scraping the poop out most days and just when it starts to dry up, it rains again Might try a bigger tarp and some guttering to catch the water rather than it running in to the run. Just not sure what to do right now but it’s driving me batty...