I am not quite sure how to think about your question. In part, I don't have any idea where you are coming from or what degree of training you have in philosophy. I think one issue is that it's hard to define the "core of philosophy" so many of the people writing sociology and political science as continental philosophy do so because they think that is the core. Or to put it another way, many of them are engaged in a critique of standard notions of metaphysics and epistemology (I studied this for several years before deciding on modern philosophy as my AOS because I don't think their critiques are as effective as the hype machines make them out to be).
For instance, I take it to be central to Foucault's history of ideas approach that he doesn't think we're doing much other than playing language games so we should be honest about things are moving. A similar historical approach with different results is taken by Charles Taylor. In both cases, there's a Hegelian heritage at work there. (On the analytic or "post-analytic" side, you may want to compare this with Richard Rorty).
If you're looking for continental thinkers doing "metaphysics/ontology" or "epistemology" however they might define those terms or however similar their projects might be.
Then I might suggest Martin Heidegger and his text "What is Metaphysics?" along with Being and Time as good intros to continental approaches to these questions. A major movement that builds (or at least grows) on this in epistemology is hermeneutics with Gadamer being a key figure.
Alternately, you could look at the phenomenological tradition more broadly going to back to Husserl and then forward to a variety of thinks including Jean-Luc Marion and Jean-Luc Nancy. Levinas is hard to follow but also kind of about "metaphysics" depending on what you mean by the term (and falling in line with the phenomenologists in some respects).
Sartre's Being and Nothingness is about epistemology and is an elaborate (and winding and confusing) critique of Hegel and several other thinks about the nature of knowledge. (It was also parodied by the philosophers of language on the analytic side).
Derrida is also engaged in a kind of critique of knowledge project.