There are some over at Shoutcast, just enter Christmas into the search field.
If clicking on the yellow "tune in!" button doesn't automatically add the station to your iTunes library, here's what to do: ctrl-click on the button, copy address to clipboard. Go over to iTunes, pick Advanced->Open Stream and paste in the URL.
(Just some explanation: the radio directory in iTunes is really just a list of shoutcast-type stations, you can use any MP3 stream.)
Last year there was a fairly long list in the category labelled "Holiday", which stayed active through July. Then they pulled it and it's not returned yet. Sux!
The Holiday category was there when I looked in iTunes the other day but I clicked on it and it disappeared. It wasn't hard to find an internet station that played christmas music.