Adult Literacy - Where are the books?

I've really been struggling to find books for our adult learners who have a reading age of 5-8 years. They are only just beginning to read and there doesn't seem to be anything on the market that appeals to an adult reader in terms of content but is simple enough that they can actually read it. Am I missing something? Why has no one really produced any books of this nature? Surely there are people all around the world who need such books. Adults learning English for the first time, people who dropped out of school and never learnt, teens who were slow to get started. It seems obvious and yet here I am desperately searching and finding nothing. I did have some hope today when I met a rep from Ransom Books. She showed me some of the things that they were publishing and it's the first time I've even come close to finding anything that might suit. The best fit seems to be Dark Man which is aimed at teens/young adults.

Surely I can't be the only one experiencing this problem! What are other people using?