If you like to read classics, visit Guttenberg. Other than that, the Internet Archive has some rare books also. I've found two such rare books from that site.
If you're a beginner, Don't go down on that road. Read physical books. If you did, It will kill your enthusiasm. Most of all, start speaking English. Speaking is the hardest skill to achieve among others. This is a book group based in Panadura. You can buy import books cheap here.