Help with sourcing a tap fixing

[tvmo]

Hello,

I'm trying to source a fixing for the following tap:

part I'm after is a brass, threaded, barrel-shaped fixing that screws to the bottom of the tap. It feeds through the worktop and is held in place by a nut screwed onto the fixing under the base of the worktop. The problem I've got with the fixing that comes with the tap is that it is too short to protrude through the bottom of my worktop so I need it to be longer. The link shows the tap and has a diagram of the fixing which is indicated by the number '45'.

I need the fixing to have a diameter of 30mm and a length of at least

50mm. Can you help please?

I know I could countersing the fitting but I really don't want to do that if I can avoid it.

Thanks very much,