Sorry to bring this back from the dead but I've never been in this section of the forum before.
Wikipedia points out that a lot of the ingredients of the Vesper have changed their formulas since Casino Royale was written in 1953 and gives some tips on how to make a Vesper that tastes like the original would have-
Since both Kina Lillet and Gordon's have been reformulated since 1953, substitutes can be made that attempt to recapture the original flavour of the drink:
To recreate the original bitter flavour of Kina Lillet, add a dash or two of orange bitters, Angostura bitters, add a pinch (1/16 of a teaspoon) of quinine powder or use a mix of Lillet and the bitter China Martini, which also turns the drink light golden, as described in the book.
Alternatively, it has been pointed out that Cocchi Americano has a similar flavor profile to the classic Kina Lillet and is an acceptable substitute.
For a more traditional flavour, use 100-proof Stolichnaya vodka to bring the alcohol content of the vodka back to 1953 levels.
Likewise, Tanqueray gin provides the traditional flavour of 94-proof gin; whereas Gordon's Gin was reformulated to less than 80-proof.
A modern cocktail glass, which is larger today than was common in 1953, is often substituted for the deep Champagne goblet (see Champagne stemware for the original look of the drink)