Get a hold of the BLM themselves. The local Riverside/San Diego counties headquarters is right near where I work and it was full of really nice people. The clerks were nice and called the Ranger out in the field when I was tracking down our ability to use registered weapons on BLM property. He told me of a couple of local places to shoot even.

Click on the area you're looking for and chat them up - I found the people there to be really nice.

www.ca.blm.gov/fieldoffices.html