Link building isn’t some mystical SEO hack. Building links is straightforward: find relevant sites that have a reason to link and convince them to link.
Why would another site link to yours? For a variety of reasons: because a relationship already exists; because they’re talking about your business/products; because you’re a valuable resource for their audience; or because you’re involved in the same community events. These are other reasons, of course.
Links represent a relationship and connection online. If you want to build links without creating content, then you should be looking for opportunities created by existing relationships and connections.