I tend to buy a lot of parts via Ebay. Always find what you need there.
Autodoc.co.uk is also an extremely good place to compare prices from different parts manufacturers, and they list part numbers too which makes seaching for bits really easy on the wider web.
Always worth a ring, are your local motor factors. Ask for their best price, or any discount for the hard up? Some factors are happy to discount to get the business so worth a punt in my experience.