Someone once gave me this advice as an undergrad: Get in your professors' faces (in a good way).
Faculty have office hours, take advantage of them. Hang out after class to further discuss something in that day's lecture that interested you. Befriend department secretaries, they're the gatekeepers. Get involved in the department outside of the classroom. My undergrad department had clubs, mixers, etc. No, you don't have to be "researching hepatitis" to get on a prof's good side, but showing an interest in their field of research doesn't hurt.
I'm not sure where you're at in your career and LS application process, but I'm 7 years out of my undergrad and had two former profs I was close to and kept in touch with who were happy to write me LoRs. And I could have easily asked two others.
Bottom line, it's all about networking, which is a skill all law school aspirants (presumably) have.