This is the closest thing we've found, but it's pretty sparse on details. The kids need to know how it was made, what materials were used, where it came from specifically, and so on.

Most museums with collections online will give this information. For example, the Metropolitan Museum of Art's Timeline page on Ancient Greece.

I would highly recommend Google Art Project. You can easily search by place, date, material, object type, etc. Not every item has a good description, but the majority have rather informative background info from the museum that owns the pieces. You can also create your own galleries/collections of objects, a very helpful tool in a classroom setting.