DK books are definitely a staple in our house and they are well worn. Unfortunately growing bored with them. Have exhausted the public library. Just wish there were more history based resources I could access for after schooling like all the great math ones I have found for my other kids.
From one bibliophile to another, while I can't recommend a history series for non-readers, sometimes it is fun cobbling together a collection of different books including those with pop-up features, richly illustrated, and/or having artifacts like letters in pockets.
In case he may not have seen these yet, and if you think these may be of interest:
1) The White House In Miniature, by Gail Buckland, 1994. Great pictures tell the story for now, great text for later.
2) Timechart of World History. Several versions and title variations available.
3) The Story of the Statue of Liberty with moveable illustrations (pop-up book).
4) Lewis and Clark on the Trail of Discovery: An Interactive History with Removable Artifacts (Museum in a Book)
Did you know that public libraries can arrange inter-library loans to bring in books from collections held at other libraries?
Another economical alternative may be Half-Price Books, Goodwill, and rummage sales (especially school fundraiser rummage sales) for interesting history books.
There are online resources as well, in case that may work for your family. Many are easily found through search engines, including...
1)
http://www.bbc.co.uk/history/forkids/2)
http://www.kidsolr.com/history/3)
http://www.havefunwithhistory.com/HistorySubjects/
