This is the one that advertises on ebay, they are from France....There was one advertising custom seats for the 1300 on ebay last year. I don't recall the name, but maybe they're still doing it? or someone from the UK can chime in.
http://www.topsellerie.com/@EN-FR/seats-petrol-tank-covers-tank-bags-leg-handgrip-covers-motorbike-scooter.html