Were they part of a drainage channel?

If so, you might find some at a second hand building parts centre.

Stu: Field Tiles? Plumbing supplies or Mitre 10/Bunnings etc, perhaps.

Perhaps a second building supplies place that sells stuff that has been ripped out of out houses.

They are a drainage channel to the side of a footpath. There's 20-30 metres of it and the 5-6 metre bit I have to re-instate is mid-way along the length of it.

I thought that changing to plastic type stuff would be bad not only for inconsistent looks but also a challenge to make the water flow nicely between the differing profiles.

Awesome - thanks @uncledave and everyone. Google is actually useful once you have the right search term .