For those of you who live in Houston, you probably know there is a large Asian community near Beltway 8 and Bellaire on the west side of town.
I was over there today, as I often am for good restaurants, and found a great store called Fit Japanese Household Items. It has a TON of Japanese items (virtually all in Japanese and no English). Containers, bags, boxes, cleaners, supplies, etc.. The list is endless.
Regarding bentos: they have MANY bento supplies (cutters, molds, dividers, etc), but a limited selection of actual bento boxes. The ones they have are geared towards children.
I encourage all to check it out. Their website is below. The place was beautiful and clean and the staff was very friendly.
Store Website: http://www.fitjpstore.com/ 
Yelp! Entry: http://www.yelp.com/biz/fit-japanese-store-houston