Examples of SouthernSearch (Buley Library's library catalog) subject searches you can use to look for government documents on taxes include:
Capital Gains Tax Law and Legislation United States
Flat-Rate Income Tax United States
Income Tax Deductions United States
Income Tax Law and Legislation United States
Inheritance and Transfer Tax Law and Legislation United States
Taxation Law and Legislation United States
The online Catalog of Government Publications indexes U.S. Government publications from 1976-present.