It's this sort of thing, but the male bit?:
ISWYM, probably the only way to get hold of one would be buy an extension lead for ~£18 or maybe £14 from a Flymo spares place:
I'd just use the above flex connector to make an adapter then securely attach the plug to the handle of the mower.
If you did buy the lead then a 3 pin plug could be wired to the spare socket and cable, as a spare or for Ebay.
cheers, Pete.