Using PsychInfo, find profs doing research in your area of interest. Write to them directly and ask them if they need assistance. If they say no, ask them whether they know anyone who does. Also, join the listserves of APA divisions or other professional societies that match your interests. Look for postings about RAs, or if you see postings for a postdoc, write to them and ask whether they also need RAs (usually a postdoc posting means they have a grant, which means they might also need RAs). Be very persistent! It's tough, but you'll find something!