Libraries, particularly research libraries, are just about always the best source of information. Anything worth its salt that you will find online will be citing texts and documents one would find in a research library.

Your best bet is to dig deeper in the Library. Don't only utilize the sources you have but maybe even check the sources that they cite. You may very well be able to dig up a very interesting primary source or document or maybe find another text relating to a particular area of the subject you are researching. Sometimes it can be tricky to find a good starting source but once you do, you can start to dig deeper and deeper into things.

As for international relations/cultural history I don't know of any in particular off the top of my head but your best bet would be to narrow down exactly what you're looking for first as this is an incredibly wide range of study.

JSTOR can be a bit of a challenge for finding historical articles. THey have a great list of interdisciplinary journals, but sometimes I've found that what I want get buried under what I dont want.

If you are specifically looking for historical articles, I would recommend to you America History and Life or Historical Abstracts. AHL and HA are great databases for those kinds of sources, and has some nice search features. AHL focuses on American topics, while HA does non-American. Both should be available with an Ebsco subscription but YMMV.