Normally I would say the link below:
http://www.giantshark.co.uk/voltage-...-p-406229.html
Unfortunately out of stock and the model shops charge £6 to £7 for these.
Alternatively buy cap from RS and solder to an old servo lead from a defunct servo:
http://uk.rs-online.com/web/p/alumin...itors/7110882/ £3.20 +vat for 10
you can get 4700uf from maplin but they are 16v so bigger and harder to find space for them
if you haven't got a spare socket in receiver you can buy a Y splitter from Giant shark, cut one socket off and solder your capacitor to that