I've had my eyes on these shoes for quite a few months (hat tip to some reply in an Ask Metafilter post). Unfortunately, they are neither marketed nor sold in Japan, at least according to manufacturer's website. Luckily, Michigan had the most retailers of any state I was planning to visit, so I was feeling lucky about my chances of snagging a pair.
Until I remembered that I was visiting WEST Michigan, where everything is closed early on Saturday and all day on Sunday. Unfortunately, we were about 30 minutes too late to get fitted at The Outpost of Holland, so the next day we drove to the Gazelle Sports location on the east side of Grand Rapids (where stuff is kinda-open on Sundays). I got my size fitted and everything, but they unfortunately only carry the classic model, and I want the KSO (keep stuff out) model.
And now, a brief aside on classic versus KSO models of the FiveFinger shoes. The choice between the two is mostly a matter of taste: ostensibly the KSO, with a covered mesh shoe-top can keep stuff out (that's where the KSO name comes from), but I mainly avoided the classic model because it looks like a ballerina slipper. Judging by how much attention my muted solid black KSO's attract, the constant sideshow afforded by classic model may be just too distracting to get used to.
Still determined to get shoes while in a country where they retail, I returned to the Outpost on my way out of Michigan and they thankfully carried the exact color and model I wanted. Unfortunately they did not carry size 43 (which is probably my real size) so I got a 44 instead. This would be a huge problem for classic model, since there is no strap to keep the shoe from flying off your feet. Fortunately, the slightly too big size has not been too much of a hassle yet, aside from more frequent friction (more on that later).
If you live in America but your nearest store does not carry the exact model that you like, I recommend fitting for a classic model and then ordering online direct from the manufacturer. This way, you can be sure that it will fit fine without extra-tight straps, and Vibram (manufacturers of the shoe) has a generous return and exchange policy should you find that the sizes do not work out to your favor.
If you live in a country without an official retailer, your options are a bit more limited. Over at Birthday Shoes, there is an effort to collect data on VFF shoe size and how it correlates to actual foot length and US/UK "normal" shoe sizes. Also, used pairs of shoes do show up on Ebay from time to time, so that is another option which may work out in different countries.
Above all, make absolutely sure that you have the right size, because it may be difficult to exchange them later. After using them for a few days, they will begin to mold to the shape of your foot, and whoever sold them to you may be hesitant to take them back after they adopt the shape and smell of your feet.