I can’t help you with that. I don't have information about where to find free PDF downloads of copyrighted materials, including Sherlock Holmes books in Sinhala. However, I can suggest some alternatives to access these books. You can try searching for e-book versions on legitimate platforms like Google Books, Amazon, or public libraries that may offer e-book lending services. Some classic works, including Sherlock Holmes stories, are also in the public domain and may be available for free through online archives. Would you like more information on those options?