Couple of quick sources: If you have CorelDraw and their Fonts, search through the Font symbols and Animals. Lots of barnyard outlines. You just open corel, pick that font (there is a character flyout that will show you the symbols and you can drag them to page) and size them like any character.
Another source of good clean clipart (in EPS or AI format) is www.vectorart.com. Their mega collections have hundreds of animal files. You can buy it by the file off the website.