Can you buy bulk shifting/brake cable for road bikes? Is it possible to buy bulk amounts of shifting/brake cable for road bikes? It would be nice to just have a spool of wire that you run onto your frame and then cut off only as much as you need. 

A Google search for "bike cable spool" doesn't really result in much, surprisingly...

How do bike shops deal with this? Surely they don't buy individual packs of cable for every bike do they?

I know you can buy cable housing in bulk, so I was surprised when I couldn't find similar for just the cable...
The problem that you'll likely run into is the stop in the lever/shifter ends. I'm not aware of any systems that will accept bare cable at this end:

If you wanted to pair your spool of wire with some sort of crimper (or go all out with some sort of mold/press), you could make your own - but investing $3,000 - $30,000 on some machine that melts metal on the end of the cables probably isn't worth your while.
I don't have much experience with bike shops (I buy most everything on eBay), but I would think they have boxes of these cables packaged in bulk like this: