I'm in a very small town, and I use eBay for most of my bento accessory purchases. For a good-quality bento box, I would suggest casabento.com - if the site loads in French, go to the top right and click to load it in English (unless of course, you can read French, in which case, don't worry!).
I also use regular food storage boxes - if they're shallower rather than deeper, they'll work nicely.
en.bentoandco.com. This is my favorite site to purchase bento boxes and supplies. There are also good deals to be had on Amazon - just do your homework. Collecting boxes and accessories is addicting - I've had to sell off most of my stuff because I simply don't have the room for it!