They just carn;t be found, are not made anymore for the u.k market.
You can get them from Ebay and other places but they will not be a uk type fitting, bc & es.
their height was mid 60's when people used them with 1 bulb in, and they use to connect other things to it too like iron, t.v
Just use the single light fittings, £1.92 inc vat from screwfix