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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.