Another possibility is to review the literature you've found to see what data they've been using. You may be able to track back the data to a publicly available dataset, or contact the researcher to request their dataset.
The following are databases open for research use and are not restricted to Iowa State affiliates. If you need access to data not found on this list, please email me.
If you have a question about data that you are creating in the process of your research, please contact: datashare@iastate.edu
Many associations, councils, and centers may provide data or statistics, as well as reports.