A liner is a liner... most welding shops should carry them "Off the roll", we have one in nottingham - "giz 3m of plaggy liner please" and he cuts it off !!! I bet its the same with metal ? If not, theres a few locall (ish) that do pre cut ones... for about £7.
I was going to swap mine too, but dont weld a lot, so imagined that it may corrode.