I believe the Cometic gaskets are only available from America and are not imported into the UK I have one that was given me on the timing side of the Comet it works very well I have to say.
I am using the doughty seals from Neil Videan that also work well.
All the above need to be made easily available in UK the problem with imports is the additional charges by our post office currently an £8.00 handling charge and then customs duty at 20% added to any purchase over £35.00