I'm not sure of any specific places that offer free anime light novels without any legal issues. But you could try looking on platforms that aggregate free content from various sources, though the availability might be limited and the legality questionable.
One good place to start is BookWalker. It has a diverse selection of anime light novels. Another option is Barnes & Noble's online store. They might have what you need. You could also search on Google for specific anime light novel titles along with the word 'read' to find more sources.
You can try looking on online platforms like Amazon Kindle or websites specialized in light novels such as Webnovel. Some libraries might also have a collection.
You can try some public library websites. Many libraries have a digital collection that includes anime - related light novels which can be borrowed for free. Also, some official author or publisher websites may offer free samples or even full - length light novels on a promotional basis.