cannot seem to find the gas cartridge anywhere.
Have you tried Boots? See link below. You could get some loyalty points at the same time to redeem against your next purchase :-) Good luck!
You can find the cartridges in and argos store or argos online. http://www.argos.co.uk/static/Product/partNumber/4417297/Trail/searchtext%3 EBABYLISS.htm
Hi..try this one http://www.johnlewis.com/230476309/Product.aspx It does have model numbers that it won't fit but it doesn't seem like yours is affected.