I'm surprised you haven't seen them anywhere. Every garden centre within a 25-mile radius of me has or has had them. Lots of online plant sellers stock them too - do a Google search to find them. :)

You could visit Goy's garden centre section to find suppliers.

Let me know if you still can't find it and I'll try to get youa bit when it dies down. Sprawling everywhere at the moment. It looks great planted with light orange crocosmias