While I don't know much about SYRIZA, I believe it is a coalition of left wing organizations, and it may be a bit too blanket of a statement to call it the Left Wing of capital (although it seems to serve that role as the new main opposition party with more toned down policy prescriptions).
I can't help point you in the direction of good sources, but I would say that a brief history of their formation and a look at the factions (and how they interact to shape the overall organization) will help with your paper.
And of course it depends on what kind of class it is, but you may want to avoid too much usage of rhetoric that is often associated with Marxist political publications, as academics tend to frown upon that.




