well .........
what you define like "HD video" is no more, no less than a video with a high resolution and a low compression ....... there is no "HD video" definition .....
don't think that exist such a site ....... because the video are very big in diskspace .......
the blueray format for example ...... we are talking of hundreds of Megabyte each minuts ........
so a single clip might weight between 1~2Gb
Thru a good video source and good filters you might approach of the quality you ask ......
don't know if it's authorized to give links in this forum ....... i'll try
one high quality video/trailer that might help you (but it's in windows media player format) :
http://rd.yahoo.co.jp/tokushu/5cm/tease ... 80_720.wmv (official link of the trailer)
it's the official trailer of a japanese animation named "5cm" in a somewhat HD mode
official website :
http://5cm.yahoo.co.jp