So your EGR valve doesn't have an internal vacuum port? What about swapping the intake manifold for an earlier model G63B? The EGR valves on them are 80% cheaper. I know you are tied to Cali emissions so this might be a no-go for you. The only other option is hell dodgy but not impossible - pry the top off the valve and swap the diaphragm from a more readily available unit. I see guys fix their own vac advance servos on historic UK vehicles so it could theoretically be done