China most probably but you'll have to buy 1000 of them.
Give up - live with it or buy a new kettle.
Nobody is going to get rich by stocking plastic bits for kettle lids. Your search may be futile but you might try these people...
http://spares2go.co.uk/browse-BREVILLE-KETTLE-Spares-m114-t13.htm
Good luck..., January 2015