You can try looking for it in local bookstores that specialize in light novels or Japanese literature. Sometimes they have a section dedicated to such niche novels.
You could also try searching for it on second - hand book websites. There are many platforms where people sell their used books, and you might be lucky enough to find the 'chtholly light novel' there. Additionally, if there are any fan communities or forums dedicated to light novels, you can ask there. Members might be able to point you to where they got their copies, whether it's from a small independent publisher or a more well - known source.
Online platforms like Amazon might be a good place to start. They often have a wide range of light novels available for purchase, both in physical and digital formats. Also, some e - book platforms specifically for Japanese or Asian literature could have it. Another option is to check out some specialized anime and manga stores, as they sometimes also carry light novels.