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www.istockphoto.com has some stuff
mostly you will just need to get some generic clip art packages and start making your own, using elements from various clip art images.
I just found this link and was basically going to ask the same question. I had found a few istockphoto graphics but wanted to modify them for a t-shirt design. Should I only pay for the basic licensing since I want to modify them. I really can't afford the extended license.
The Art Explosion clip art libraries sold by Nova are a good foundation for a clip art morgue. They are the bargain of the century. The CD libraries range from 50,000 images to 500,000 images. Excellent mixture of vector and raster images.
how to get stock vector grahpics 
