While checking through the Granger Industrial Supply catalog for
vacuum pumps I came accross a device called a vacuum generator.
(granger cat. #387, pg. 2441)
Based on the description I'd say, you'd probably get
dissatisfied with it
before long. You'd have to have about a 3-5 hp air compressor to
supply enough air to generate the vacum in a timely fashion.
You'd probably also
need a large (aprox 20 cu ft) auxiliary vacum tank between the
generator & the vacum chamber.
Probably the best vacum pump for the caster, is one rated for
refrigerati on service. They come in several sizes & you can
usually get them at your local refrigeration parts supply house.
I've seen them listed in the "Tools" section of the want ads from
time to time. The refrigeration supp ly houses can also provide
vacum pump oil & service for the pump if it's ever needed.