I have a HPI Savage and a Losi Mini-T... I usualy find that microtechracing.com can supply most spares I call them for, even if it can take them a week or so to get them in stock from their suppliers.
modelsport.co.uk are also pretty good and
www.apexmodels.com is a great source for HPI stuff.
on the flip side, towerhobbies.com ships to the UK for a reasonable price and you will save a lot on the $ to £ conversion....