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.
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.
You could look on dedicated light novel websites such as BookWalker or J-Novel Club. Libraries might also have digital collections of light novel anime that you can access with a membership.