Vertical 2D Shoot em up Sprites / Sprite rips

This seemed the most logical part of the site to put this request. Basically for my university degree, I am working on a vertical shoot em up ( I am studying a course on Games and Graphics). To cut a long story short, the game is finished, but I am no artist and have really poor designs for my bosses and enemies. Would anyone happen to have hold of or know where I could get hold of some nice 2D shoot em up sprites, such as these found in Tyrian or Raptor. Any help would be appreciated.

this place has some 2d shooter sprites http://www.panelmonkey.org/category.php?id=1