You can also check out J-Novel Club. They are known for translating and distributing various light novels, and there's a good chance they have 'Rebuild World' available. Additionally, some local libraries might have physical or digital copies that you can borrow.
Comiket, the Comic Market in Japan, is also a place where you might find doujinshi (fan - made works) related to 'Rebuild World' light novel, and sometimes even official merchandise or early versions of the novel. However, it can be a bit difficult to access if you're not in Japan.
One popular platform is Amazon Kindle. It has a large collection of light novels including 'Rebuild World'. Another option could be BookWalker, which often offers a wide range of Japanese light novels in digital format.