If its for a kid down the street, I'll bet he'd be happy with the bike even if it didn't have a front shifter. Maybe give him the bike, and he can save for the front shifter if he really wants it. If you really want to put one on it, there are some inexpensive ones available online:
http://www.nashbar.com/results.cfm?s...t%20Derailleur
Cables for a 'generic' bicycle can be bought fairly cheap at your local sporting goods store that sells bicycles. I buy them at my local Sports Authority store as a packaged set for the entire bike (brakes and shifters) for less than $10. I wasn't using the front derailleur on mine commuter so I just took it off since it was pretty rusted out.
How you route them will depend on if there are braze-ons on the frame. They usually run through a housing/tube to a braze-on up near the top of the downtube, then under the downtube to the BB (exposed), then go through a rubber housing/sleeve up to the derailleur. The 'generic' cables usually have enough tubing so you can replace whats lost or damaged, or you can just use the cable in the housing and zip tie it to the frame.