ProPublica’s Nonprofit Explorer site allows users to do full text searches of every US-based nonprofit’s Form 990 filed since 2011, provided the nonprofit filed electronically. ProPublica says that the IRS reports that about 2/3rds of nonprofits now file electronically.
The IRS makes the Form 990 data available in XML, making the full text search very robust. On its site, ProPublica uses a system based on the IRS e-File Viewer to reconstruct specific Form 990s to display as tax filing forms.