Champagne is a sparkling wine that, according to French law, comes from the Champagne region of France. Sparkling wines, of course, are made all over the world. Most are naturally carbonated in the bottle via secondary fermentation, and require aging, riddling, and disgorgement over a long period of time.
You can force carb a white wine in a keg to make a sparkling wine. I think the only cost effective way to do this is to make your own white wines. Making wine from grapes is a fairly involved process that requires some effort and practice to do well, but there are a lot of good quality wine kits that you can buy that would most likely make great sparkling wines for the kegerator.
I plan to do this myself sometime next year after I make some more white wines. The only one I have on hand right now is a Gewurtztraminer that I don't think would make a great sparkling wine.
I think you'll need to pressurize to about 35 psi.