There is a "spacer/sleeve" inside the rubber bushing which the bolt passes through.  It sounds like the bolt has sized/rusted to the sleeve.  The answer is lots of penetrating oil / WD40 / Liquid Wrench / etc....   You might also try heat (propane torch) on the bolt, cover not to heat anything else (ie. brakes, brake lines).   

Out of curiosity do you have forged lower control arms or stamped ones?  it's just different in terms of how you get at the bolt.  In any case you might take "something" like another bolt, line it up with the end of the bolt you're trying to remove and try to bash it out with a hammer.  Just something to break it's bond with the sleeve inside the rubber bushing.

I'm not quite sure how you would cut out the bolt...  but if you do you can order the bolt by part number (see image attached the email I sent you only not the list)  I think it's N0401611 

My personal favorite for random little dealer only parts is http://www.vwdiscountparts.com  but I checked and Bus Depot has it too.  Any of the major online shops could order it for you.

-Jon