It's from a company called Uschi van der Rosten....Uschi´s high stretch elastic rigging I got mine off eBay but its available in a lot of online and probably LHSs
Cool Steph and you're in luck. Fundekals released a Mk.I sheet with markings for no less than 22 aircraft. Now you just need 21 more...fundekals - Spitfire Mk.I Preview
I'm of the understanding that there is just the one kit from Airfix. My pre-order is for the 5135 kit and it's the low back which can be built as the FR.