Griffith Observatory is located at:
Griffith Observatory 2800 East Observatory Rd. Los Angeles, CA 90072 Phone: 213-664-1181
You can also contact Dave Nakamoto at JPL for additional information (firstname.lastname@example.org or 818-354-5328).
The Los Angeles Astronomical Society along with Griffith Observatory are also planning to have additional viewing sessions of Comet Hyakutake in late March, but the exact dates are still yet to be determined.
Comet 1996 B2 Hyakutake Home Page