You can search in Google Scholar or other scholarly article databases using your topic keywords and adding GIS or "Geospatial data" to your search. This might help you locate researchers doing work in the area, and their citations might lead you to more sources of data you could try to track down.
What are open data portals?
Some government entities make their data available to the public using open data portals. These portals may contain geospatial data sets to download.
How to find open data portal
Barriers to open data portals
Open Knowledge International notes three major environmental constraints that cintribute to a lack of openness in government data sharing:
"1. Lack of capacity of government to maintain infrastructure and websites; incomplete and inaccessible published official information.
2. Limited open data knowledge from the respective government officials.
3. Limited capacity and open data knowledge of CSOs to take advantage or to ask for open data."
Some examples of open data portals
What are data repositories?
Data repositories host research and other data for long-term preservation and archiving. They may be hosted by universities/colleges, non-profit organizations, for-profit companies, non-governmental organizations (NGOs), etc. They might be broad in scope, or they might organized around a specific area of reseach.
Some examples of data repositories