I don't know how to 'link' things, but if you go to ebay and search 'altenator vacuumpump' a slick gizmo will pop up from an industrial application that is an altenator with a vacuum pump on the backside. A little checking around and you'll find them for very reasonable money. It looks like it bolt right in where a 12v altenator would go. I suspect it would create vacuum at low rpm, I don't know for sure.
