Below are web sources compiling quotations. As quotations are often wrong and online sources can be of uneven quality, be sure to verify the accuracy of the quotations found therein.
"This book contains a collection of 2,051 quotations on taxes generally, the legislative process, government, progressivity and equity, exemption, collection and administration, the power to tax, and avoidance, evasion and planning."
Sources for Tax Quotes
Judicial opinions can be a source for quotations on tax. Casebooks from tax classes might point you to more meaningful quotations therein.