As mentioned in the comments, I found a resource that has a myriad of spectral samples of just about all minerals (including rust) - The RRUFF Project website, where it contains
an integrated database of Raman spectra, X-ray diffraction and chemistry data for minerals.
This site has a searchable database, the only (albeit minor) downside is that it does not allow for generic terms such as 'rust', but rather, the actual chemical names such as goethite - a main component of 'red' rust.
Raw spectral data can be downloaded from the pages.
If there is difficulty in determining the real name, then WebMineral.com can assist, through a search facility that takes the chemical name and provides mineral names.