https://cpc.farnell.com/univercell/d...-5v/dp/BT05682
"Univercell DB8014 Alkaline LR 40 cell battery", £11.78 + VAT, currently 5 in stock. I found it be googling " flag battery".
Evidently not LeClanche technology, but an alkaline substitute of the same dimensions.
PS post crossed with #55