Shinzi Katoh bento supplies online
Whenever I use the little apple shaped mayonnaise container in my bentos (as I did in the most recent bento no. 48) I always get comments or emails asking where they came from. It's designed by Shinzi Katoh, a very popular graphic designer and ilustrator in Japan. Of interest to bento fans is the fact that he has designed several bento boxes and accessories.
You can find his bento boxes on eBay, but if you want to avoid eBay there are at least two places where you can get them. The first one is the online shop section of his official Japanese site. Unlike most Japanese online stores, they do ship overseas, and have an information page in English. However, the rest of the online shop is in Japanese only, which isn't too good if you don't read Japanese. But this is the only place that seems to have the apple bento accessory line online at the moment.
If you don't want to deal with a Japanese site, there's Shinzi Katoh UK, which also ships internationally. They don't carry the apple accessories but they have several of his very cute bento boxes, onigiri boxes, water bottles and a lot more. I used one of the onigiri boxes in bento no. 37, pictured above. I haven't compared the prices vs. what eBay merchants are charging, but it might be a good option especially for UK and Europe bento fans.
[Updates:] J Flair Homestyles carries many Shinzo Katoh bento boxes, and ship worldwide. Also, as pointed out in the comments (thanks Jenn, Zora and Sile!) Sugar Charms carries several Shinzi Katoh bento boxes, onigiri boxes, and even a couple of accessories. Sugar Charms ships within the United States only.
Other online stores carry Shinzi Katoh designed tote bags, zakka (a catchall term for room accessories, stationery, etc.) and so on, but none that I've found so far stock his bento gear.
One caveat with Shinzi Katoh bento gear: You are paying for the design. In terms of usability and quality, they are generally on the same level as the 100-yen shop/Daiso type boxes. Many of the bento boxes and accessories are handwash only, and if they have silkscreened rather than baked in designs the ink may run if you aren't careful (I found this out the hard way when I ruined a very cute monkey design box). But, they are so very adorable... (Note: They seem to have improved their manufacturing processes recently, since they now have much more durable bento boxes.)