Where to find funding depends largely on your area of research. However, it is an essential part of postdoctoral training to try and secure your own funding and is expected of postdocs looking to become research faculty.
UIC has an entire office dedicated resources to finding funding. They provide UIC researchers (postdocs included!) with tools to find external funding. Specifically, UIC has a license for the use of Pivot-COS, a searcheable funding database.
For international postdocs, the National Postdoc Assocation has compiled an extensive list of International Fellowships & Grants.
Check out this article about Where to Search for Funding.
Below, the PDA has compiled a list of specific fellowship opportunities for postdocs.