Try a google search using the words:
granite lantern japanese
You should find quite a few.

Also email edzard privately. He can fix you up.

Here is a link that might be useful: edzard

I have had good results dealing with japanesegifts.com up in Minnesota. Lots of tschochkes but also a good selection of granite lanterns.

May I humbly suggest Better Gnomes and Gardens in Victoria BC? see link below

Here is a link that might be useful: Mt Fuji gardens

Hi Laurie
Are you still working on school's Garden ? ^-^ .
Greg made excelent sugestion. .........mike

A lot depends on what style - and especially size - of lantern you have in mind. They're sometimes advertised on eBay - but granite (or ordinary concrete for that matter) is extremely heavy. This makes mailing awkward & costly unless you'd find one of the more modest sizes or one made of lightweight concrete adequate.

Thanks for the suggestions. Mike, you've got a very good memory. The school I'm working with has just gotten another grant. One of the parents is going to build an entry gate and small deck, and another parent wants to donate a lantern. I'm sure they're thinking about one of the smaller ones. I was hoping to find a resource in Chicago, but haven't been able to. I didn't think of the weight issue. Maybe my best bet is to go through Anderson Gardens in the spring.
Last spring we laid out the paths, using landscape fabric and mulch, and pulled out some overgrown shrubs. The parents lined the paths with small boulders, but no plantings were done.
Thanks for your help,
Laurie