My research, and findings, on the Spitfire cockpit, were all total luck. I was given access to some parts, which had been removed from AR213 during a rebuild, and found that the colour was an exact match to the colour chip for Humbrol 90 (as it used to be, before Hornby took over production.) It appears that, 20 years ago, Humbrol matched their (then) new 90 to the colour of another Spitfire's interior, but never bothered to tell anyone; all they did was advocate this colour for their 1/24 kit. Even the "beige-green" title is no help, since the official title was simply "cockpit green." Because of this odd behaviour, Hornby's management had no idea what it was for, but assumed that it was supposed to be Sky, so they changed the formula to match that. This means that any Hornby-labelled tin is, almost certainly, Sky, but, if you have a Humbrol-labelled tin (which will have to be at least three years old, now,) with no mention of Hornby, it should still be the correct shade for a Spitfire cockpit.
I did get a bottle of Tamiya XF-71, and, although the cap appears to be correct, the paint, inside, is nowhere near the Spitfire colour. For what it's worth, the only advice, that I can give, is to find a Humbrol "Colour System," or some similar old Humbrol card, with a proper colour chip (not just a colour pamphlet or leaflet) and see if you can match one of your paints to that.
Not a lot of help, sorry.