A lot of sites say Corona kegs don't exist, but they're apparently available in some places (just really uncommon outside of Mexico). Any kegs that come in are going to have to have been imported from Mexico, which may make it more of a hassle than most places are willing to deal with (particularly for a beer that has such strong branding based on its bottle). Looking around online, it appears that larger caterers sometimes get kegs (watch their prices, though--they can get really expensive). If you live in Texas, you may be able to find a keg (see my links below for a few leads). I found sellers in Omaha, NE, New York, and California (see my source links), but some of them are caterers for convention centers--you may not be able to buy a keg if you aren't renting space from them too. In most places, Corona in a keg seems to be almost unheard of. If you live in Texas, or a big city in another state, you may be able to locate a supplier by calling some liquor stores and caterers. Otherwise, you're probably out of luck.

No, they are not available in the US as far as I know. If they were to ship them, they would have to come through Texas and would probably go bad by the time they got to any store. Corona just wants people to drink their beer the way it is. Sorry!