What if you find a smog pump off like an 80's Dodge truck and modify that?? I know of some rock crawler guys that have used them as like mini air compressors to fill up small 10 gallon tanks on their rigs just in case they knock the tire off the bead or have to air up after running low pressure for the rocks. They just use some sort of regulator on it.
Essentially it sucks air and pushes air, isn't that what a vacuum pump does?? So......