Hi!
Whilst Heckshers in London are helpful for most things, I discovered
http://www.pianoaccessoryshop.co.uk/
as a source of one item that would otherwise have been rather expensive.
http://www.pianoaccessoryshop.co.uk/piano-repair-parts-1228-0.html is a source of felt and buttons and action lubricant which may have applicability to tracker action instruments also.
Best wishes
David P