Does anyone know of any places that sell ceiling coving? During my youth we used to have polystyrene coving in the house

Polystyrene was banned years ago, due to the acrid fumes it produces when set alight.
The tiles were banned also, the stuff used to drip when ignited causing it to burn your skin if you were unfortunate to be in the room.

Stick with Plaster coving, much safer !!!!

So where is it sold ???

Most builders merchants have it, or can get it for you