does anybody have one going spare?

If you can work out what size it is (mine are 16mm long M5) then you can buy them form any half decent fixings co. Try Orbital fastners they are london way but will post up here for a small fee. Just measure the diameter of the screw and the length of the threaded section then youre away...

http://www.maxwilson.co.uk/

Try this place if you're near Newcastle, they have counter for trade and public.