If you are interested in finding scholarly sources, the first thing you should consider is that the gold standard, as it were, of what is considered acceptable scholarship is either books from scholarly presses or peer-reviewed scholarly journals (usually print journals). Although you can find electronic versions of print journals online, websites are normally not considered scholarly sources.
In order to search for scholarship on Gothic literature, you need to start in the online library catalogue of your university. There, under electronic resources, you will find two indices, the MLA International Bibliography and Jstor.
In the MLA bibliography, you can search for scholarship on the Gothic; search results will point you to scholarly books and articles on the topic, often with links to full text.
Jstor searches will link you to the full texts (.pdf versions of articles from print journals) of articles on the Gothic.