Is there a local pro-shop with the oscillating "Haus" machine available?

Are you talking about a full resurface or just surface prep/touch up?  How often are you doing a full resurface?  Deep scratches are not that major if they are not any wider than normal logo engraving, even in the track.  The ball will not look as pretty, but I haven't found any real performance benefit from sanding out every scratch in the surface.  If you cut that deep all the time you'll end up replacing your gear a lot sooner than need be.  I do weekly touch ups and resurface about once every 6 weeks depending on how much bowling I do...my gear looks used but not abused.

To answer your original question I have used down to 80grit wet/dry sand paper on occasion for balls with hard shells or with deeper scratches...just step it up by doubling the grit each step to get the sanding marks out of the ball as you move up....ex 80-160-320, 500-1000-2000 etc...use PLENTY of water at the rougher grits.  Hope this helps.