Nigel
You could no doubt order a set of loose fit carpets for a later model of your caravan from a Swift dealer, providing the colour scheme is compatible.
Perhaps you could persuade a carpet fitter to lay the vinyl for you? However, it would not be the same as factory fitted vinyl -ours has been laid before the furniture and fittings were put in and so covers the entire floor of the van, under the bedboxes etc.
Just worth mentioning, our 2003 Ace caravan (also made by Swift)does have loose carpets and I am very disappointed with the quality and wear on them. The pile is already looking flat & matted and the carpets also attract 'lint' from other fabrics, such as socks, beddding etc and is very hard to vacuum off.