Roof slates/tiles (Presteigne LD8)

I am looking for some old slates or pantiles I can use to divide up a herb garden. I need about two dozen 40cm or more long (if pantiles I guess I’d need maybe fifty as won’t be as long. Photos as an example. People might have ideas for something else good!

Obviously can be damaged/unusuavble ones as one edge will go in soil so a broken offf corner is irrelevant.
Can you help with this request?
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