I know the one you mean, Nactel. Not something that's used today though.
Obviously a very "local" material. I think your only solution is to do what they did when it was built .............. get out your bucket & spade ;o)
A bit of a long shot ........... assuming you are near the sea, do they use sea-sand for building around there? It would be dredged, then unloaded at the quayside, and washed (to remove the salt). That might be a place to look ............... if there is one.