One website that may buy novels is BookBaby. It provides services for authors to get their novels out into the market and in the process, if your novel meets their criteria, they could potentially buy it. They also offer various marketing and distribution options for the novels they deal with.
Well, one way is to check out popular online marketplaces. Another option is to see if there are any import bookstores in your area that might carry them. Also, you could look for groups or forums of light novel enthusiasts who might have tips on where to find them.
Some Japanese online bookstores like Rakuten Books or Kinokuniya might have what you're looking for. They specialize in Japanese literature and could offer the ebook format you need. Just make sure to check their availability and payment options.
Some Japanese bookstores have an online presence and could offer easy Japanese novels. Another option is to look for second-hand bookstores, you might get lucky and find what you need there.
Specialized gaming stores, both physical and online, might be a good option. Some examples are Play-Asia or J-List. These stores focus on Japanese games and media and are likely to have the visual novels you're looking for. Also, check the official websites of the game developers, as they might have direct sales or links to authorized retailers.
You can try online marketplaces like Amazon or specialized online bookstores that focus on Japanese literature. They often have a wide selection of light novels available for purchase.