I realize this is an old thread, but since I'm currently re-reading My Lady Nicotine for the umpteenth time, I thought I'd tack on some thoughts.
As others have already noted, Barrie was referring to the Craven A Mixture. Do keep in mind, though, that he was writing for entertainment; I'm guessing he exaggerated the superb qualities of the blend for effect.
McClelland does make an "Arcadia" as part of their 221B series. I last smoked it in 2008, but at that time, I wrote: "Arcadia is a very well-balanced mild-to-medium English with a distinct 'McClelland' quality to the Virginias (which I enjoy) and some nicely flavorful orientals that poke through now and again. Not heavy with latakia flavor, just well-proportioned with high-quality ingredients." Barrie's "Arcadia Mixture" could win over over a man with a mere whiff, leading him to turn away from lesser blends forever. To my palate, there is nothing in McClelland's Arcadia to inspire such single-minded devotion.
Cornell & Diehl also make a blend they claim is inspired by the Craven Mixture: Yale Mixture. I've got tins in the cellar, but I haven't yet smoked this one.
It's possible that other blenders have Craven equivalents. . . but duplicating a blend like this is an impossible task to set for any modern blender. Today's crops are different, some tobaccos aren't even available anymore, and how can anyone possibly duplicate the flavors of a fresh tin of Craven Mixture when it's been over 50 years since such even existed?
The search is terrifically enjoyable, though! For me, my "Arcadia" is Penzance, a blend that tastes like no other tobacco I've ever smoked. It hooked me from the very first bowl. (Bengal Slices is/was similar, but it lacked a certain spicy zing that fresh Penzance has.) I think each pipe lover will have their own Arcadia. . . and I think that's one of the things that makes this hobby so enjoyable.
Bob