All the usual suspects are showing them as "No Longer Available", and there's some comedian on eBay who is auctioning one with weeks to run and a starting bid of eight quid ;-)
Iād nip down the local breakers with a pair of wire cutters in your pocket š
My local factors had a generic sidelight bulb holder which fits in the hole but the connector was wrong for the plug. A bit of carving away of the plastic made it fit.