I had the same problem as you. Pretty much all the classes I took were large lectures and I never went to office hours or anything. For one recommendation I went to a professor from a small class where she would at least remember me and the project I did. Aside from her, I had NO interaction with any other professor and needed a second one. I was so nervous, but I went to a professor who didn't know me. I picked her because her class had a lot of assignments, not just exams. I went to her office hour, told her the classes I had taken with her, gave her a copy of my assignments from her class, my resume and an unofficial transcript. Your personal statement would also be a good idea to give, but mine wasn't done at the time. She was very eager and willing to write me a recommendation which surprised me. I only talked to her for a couple of minutes, just small talk about law school and about the class of hers I took. I have no idea what the letter ended up saying. I'm sure it wasn't awesome, but it was good enough since I got into plenty of schools. If you want a great recommendation then you should try to participate in class, talk to your professors sometimes, and write great papers, but if you're just looking for a decent recommendation that won't retract from your application then it doesn't matter.