Can't speak for CXYU but LiveATC.net was fortunate that a volunteer stepped forward to offer an Oshkosh feed during AirVenture 2006. The feeder promptly pulled the feed immediately following the conclusion of the event and then went dark. Attempts to reach him through this website were met with cricket sounds of a silent, wind-blown field.
Numerous threads discussing the lack of an AirVenture 2007 feed made it apparent that, at least for that event, there is big demand for it. A few of us stepped forward to financially back a feeder for 2008 but the bottom line is that the possibility of a feed at Oshkosh requires someone located near the airport with an always-on Internet connection. Know anyone?