You could try Terry Drury for the Coopers gasket (website not up to date and doesn't offer online ordering, but price may still be a lot cheaper than GGR for a genuine Coopers kit).

Also well worth phoning (although the parts aren't listed on their websites) are Reyland Motorsport or R&BMotorsport as they may be able to provide the parts too.

Also: Motorsport Developments, Woodford Garage Motorsport (website under construction) or Amber Performance, PJ Motorsport.

Not that much help with the 'online ordering' bit, but that's not down to me, lol - any of those should offer keen prices for the bits you need.

Good luck with it