I have a few links to the places for which spending money on bentos happens many times, lol. I don't know specifically about bentos for boys, but there are some more 'masculine' bento lines out there. Particularly the Shinkansen train lines which are cute but also more boyish: cgi.ebay.com/Sanrio-Shin...cmdZViewItem

There are lots that are plain one color boxes or with polka dots, and some with things like dragonflies on them: cgi.ebay.com/Dragonfly-2...cmdZViewItem

Moolka.com has a whole line of bento boxes that have some that are more masculine, a horse, a viking, etc.: www.moolka.com/jzv/prod/1...mp+Lunchbox

One of my favorite places to buy bento boxes is Jbox.com which has my favorite Totoro! www.jbox.com/SEARCH/bento/1/

I'll see if I can think of any others, but that's all that I know of right off. I hope that helps!

Here are a few more links - to a store on e-bay again, but they have some neat bentos!
cgi.ebay.com/JAPANESE-BE...photohosting

cgi.ebay.com/BLUE-JAPANE...cmdZViewItem

cgi.ebay.com/ORANGE-JAPA...cmdZViewItem