Is there any case where an individual could file an in rem lawsuit (apparently suing a physical object, as in United States v. One Solid Gold Object in Form of a Rooster, but with an individual as plaintiff)?
Yes. This is common in admiralty cases, where a lawsuit will often be filed against a ship itself instead of or in addition to its owners. For instance, see Vimar Seguros y Reaseguros, S. A. v. M/V Sky Reefer. Quiet title actions can also be considered in rem, although that can depend on the jurisdiction and the type of action.