I think you can find assets in both Itchio and DLsite. Just be mindful of their licenses, and that DLsite is primarily NSFW.

Alternatively, there are gamedev forums (or adjacent) that allow recruiting people to your projects, so maybe you could ask in those if anyone would want to do music commissions for a game. Two forums with recruitment threads/boards I know are Fuwanovel and RPG Maker's. Plus you can probably find communities that allow recruitment, game assets commissions, and/or music commissions around here in the fediverse.