Hi Guy, to my knowledge they are not available. Did you find a source? If so, many people would be interested. Curiously on my TF21 these failed under warranty. Not aware of them being replaced again since 1967 Simon
RT told me they were originally moulded but that the mould was lost and now no longer availble as a one-piece part. They can sell the profile which has to be cut and glued to fit correctly. CP also supplies a profile to suit.