Sadly, TRF does not have a "full" catalogue for either Spitfire or GT6. They do have a "glovebox companion" catalogue for the Spitfire, and it states on their site that their "full" Spitfire 1500 catalogue is coming to the web soon.
That's the bad news. Good news is that they go by Stanpart (Triumph) part numbers, and then also by Lucas and Girling numbers. So if you know your part numbers (which you can often get from, say, Spitbits, Canley Classics or Rimmer Bros. online...or from original Spare Parts Catalogues), you can use TRF's part number search to find prices and availability.