Do I have to take both the LSAT and GMAT? I'm pretty sure that I do.
I've seen the section on the LSAC website with the 25th and 75th percentile LSAT and GPA for people accepted into each law school. Is there something similar for GMAT scores?
Yes, you will. However, there isn't really a reputable source
a la ABA that has a really comprehensive percentiles listing of JD/MBA programs. My suggestion would be to do research on the individual schools that you are considering applying to the joint program for, and then contact them directly for admissions information. That will get you the info straight from the horse's mouth and you won't waste any time trying to find an online (or paper) compilation. It might be faster and easier. Best of luck!