Try Exodus Books
If you’ve never heard of Exodus Books, you may want to check them out. They sell both new and used homeschool curriculum, in addition to a host of other books, board and card games, literature and other homeschool material. They stock over 30,000 products in their inventory!
Just today I was looking for a used copy of KONOS Volume 3 and no one, anywhere had it for purchase – not Ebay, not Amazon, Homeschool Classifieds, Abe Books, Better World Books, or Thriftbooks.
I finally found it on Exodus Books and for a good price! They also give you an honest synopsis of the curriculum so you can review it before you buy it.
If you like Rainbow Resource Center, you’ll like Exodus Books and possibly even more because of the ability to buy used, hard-to-find material.
You can search by grade level or by category for any books to go along with your homeschool. I can’t say enough good things about this company.