The first thing to recognize in beginning your search for sources is that not all of the references you find on the web are actually web sources. You can read books and professional print journals online; just because you are reading it on your computer screen, that does not change the fact that it's actually a "print" source.
For web pages, you can start your research right here at enotes. Check out the links below for some excellent reading on abortion from both the health and the societal perspectives.
For your print research I would suggest you start by going to Google Scholar, which will search through thousands of print journals. You can begin by simply typing the term "abortion" into the search box. You will probably want to limit the dates of your results, which you can control with the menu on the left side of the page. Look for results that say "pdf" in the right hand column; these are journal articles that you can read online.