I've used this very good company in Derbyshire a few times for cables and other electrical items: http://www.vehicle-wiring-products.eu/You can get single core thinwall in different thicknesses with a colour trace if you're fussy (like me) about replicating the original colours: http://www.vehicle-wiring-products.eu/section.php/198/1/single-core-pvc-thin-wall-cableClick on the thickness you want and select the colour from the drop down 'Colour' box. You can buy by the metre, 30 metre or 100 metre.