Where do I find authorized weighmasters in California?

I need a weight certificate for my pickup truck, which I purchased from a private party out-of-state. Registering it in California means that I must have a weight certificate, which shouldn't really be necessary (see "weight certificate" section at: http://dmv.ca.gov/pubs/brochures/howto/htvr9.htm), but the California DMV is hling me.