What your looking for IS available however the quality can be lacking, the lighting may be off, there's gonna be foreshortening when you crop it, loss of pixels = loss in quality. If you want quality you'll have to pay (my experience anyway) and I can't be bov'erthed so I do my own when I can. Though like I can get loads of cows - not so many snakes! So yes I do buy stocks I need.
You can get premades below:
Deviant Art http://www.deviantart.com/resources/stockart/premade/
(beware of the stockers rules and regs)
(You'll have to buy them but excellent quality)
(3D site - some free, some crap, some ok, some excellent, some payment only....)
Most of the stock sites DO have these images just search "premade images" but really...go spend time taking and learning to comp your own. It just 1) saves hassle 2) you own the copyright 3) quality is kept.
Full list of stock sites ---> http://www.bluevertigo.com.ar/