First of all, there is no real reason to buy rokushaku fundoshi. They are incredibly easy to make -- you don't need scissors, you don't need a sewing machine, you don't need any special knowledge.
Take a trip to the fabric store and buy a 3-yard piece of soft, lightweight fabric. I'd recommend cotton or muslin, the thinner and softer the better. You can pick any color or pattern you want! So if you want skulls or pot leaves or a cute red-and-white checked gingham, you can have it. I tend to go for white, sky blue, olive, or bright orange. When you get home, tear the cloth into strips lengthwise, so that they are still 3-yards long. The strips should be 10-14 inches wide. Narrower or wider if you prefer, I'd say a good way to guage the width is use the distance between your hipbones.
Scissors actually do come in handy to make a small starter cut before you begin tearing.
Don't worry about frayed edges or loose threads, these will go away after a few washings. Your new fundoshi will also get softer every time you launder it, although you'll discover that several fundoshi in the drier at the same time have the interesting tendency to braid themselves together!
One three yard piece of cloth will yield several fundoshi, anywhere from 6-8. That means fundoshi are incredibly economical as well as being supportive, comfortable and sexy. Knowing that the design for rokushaku fundoshi is over a thousand years old adds a certain cachet to wearing them, for any DIY-ers or neo-Luddites out there!
Let's say you don't want to make your own fundoshi, for whatever reason, or you would like to buy other types of fundoshi. Where do you get your fundoshi?
Honestly, fundoshi are unique to Japanese culture, so the best place to get them is in Japan. There, they are available in most department stores or at underwear shops. No more difficult to find than a pair of socks. And I doubt anyone bats an eye when someone buys a fundoshi, unlike outside Japan where interest in fundoshi is considered, well, unusual to put it kindly. So say you want your own fundoshi, but you don't want to travel to Japan. Where do you look?
I've found a number of online shops that offer fundoshi. For the most part, they are primarily Japanese, so the language and navigation on the sites can be a little tricky, not to mention trying to figure out international shipping and the currency conversion to Yen.
One english-language shop I've discovered recently is xzytes.com They offer rokushaku fundoshi in many colors, offer custom sizes, and also sell Ecchu fundoshi and Mokko fundoshi. Prices are typically $12-15 per fundoshi. Additionally, they also offer many other sorts of fashion underwear. Their site also offers a pretty good step-by-step wearing guide that used to be available on geocities before Yahoo closed geocities this past October: http://www.xzytes.com/how-to-wear-fundoshi
I've also purchased a basic white Ecchu fundoshi from jbox.com. It is comfortable and light, almost unnoticeable when you are wearing it underneath clothes. Boxers can't compete with Ecchu fundoshi for barely-there comfort.
ioffer.com and ebay.com frequently have listings for fundoshi as well. While your searching around the web, you'll soon notice that ladies' fundoshi sets have become quite the hot item in Japan, and that the rest of the world seems to have perked up and taken notice. Think about the possibility of surprising a lady friend!
Here are some links to a couple other english-language shops that carry fundoshi:
And we should not forget American Apparel's sheer jersey scarf, which comes in a wide range of colors and is 16 inches wide, 93 inches long -- or, almost exactly right for tying on as a fundoshi! Plus it's soft and a little stretchy, so it's perfect for sleepwear or lounging.
Next I'll post up some more pictures to inspire your fundoshi-wearing adventure.