Bunkermagnet
Journeyman Pro
My normal go to electrical wholesaler doesn't even do them now. I think they are a thing of the past now, and I can't remember being in a house with them fitted for years.Screwfix don't appear to have them. Neither does Toolstation.
Cheapest I've found is Wickes at £2.50 for a pack of two. Amazon are more expensive.
B&Q is £5.60 for two!
But typical price for a single gang light switch is under £1.
Makes no sense that a simple flat piece of plastic costs more than one with a switch in it.