I've got plenty. Could dig out a few for you. Any ideas on how to
post them, people? Would they be ok in a plastic bag with water in
it, like I send plants?

Yeah, I've got about a hundred or so to get rid of, but I'm on the US side
of the pond, but the offer still stands for anyone else... these range from
1/10th of an inch to over 1/2 inch... and plenty of them....