First of all, you should read all books of Harry Potter if you have not got a chance to complete these books yet. It will give you a better idea of what other stories have a resemblance with the Harry Potter.
Reading J.K. Rowling’s Harry Potter will also help you in recalling many stories that you have read in your story books in childhood or school days.
Now, you should research different authors who have written different fantasy books. The most renowned writers are C.S. Lewis, J.R.R. Tolkien, Roald Dahl, E. Nesbit and Lloyd Alexander. These writers have also produced work that, in many aspects, matches with the Harry Potter.
You can also find many other stories, especially school stories. Enid Blyton’s work and Kipling’s Stalky and Co. are the most important places to start with.
You can also find fantasy stories which have many similar things like in Harry Potter. These stories are The Adventures of Huckleberry Finn, Treasure Island and The Three Musketeers are the most famous ones.
You should also go to the children libraries in your area and ask the librarians to recommend you the most fascinating fantasy story books. It will help you in finding you good story books which will have many similarities with Harry Potter.
The librarians will also help you in finding places where you will find your desired fantasy story books. It will not only help you find story books but will also save a lot of your time.
You can also read the books of less known writers which can also satisfy you or your child’s taste. You can read The Silver Crown written by C. O’Brien which is a dark fantasy novel and will entertain you to the maximum.
You should also join online Harry Potter discussion forums where many people will recommend you to read other books which have many similarities with Harry Potter.