Anyone know how to get the Science Channel without buying a bunch of cable channels we don’t need?

Nope. The cable/sat companies don’t price like that, nor are they likely to start doing so anytime soon unless forced by the FCC. And the FCC keeps changing its mind on whether or not it would be a good idea.

Or can anyone recommend an alternate source for the Deconstructed episodes.

Check the Discovery.com website, iTunes, and Hulu.com. Otherwise just about any place that might have them is illegal.