There are many classic Mariological works online, and some of them are even in English!
This one is a defense written about 12 years prior to the Dogma, defending the teaching of the Immaculate Conception. This English translation is from 1855, one year after the dogma was declared.
A Polemical Treatise on the Immaculate Conception by Luigi Lambruschini. You can download the book as a PDF file by clicking on the gear icon.