well, the thing is, you can make one, but i dont know how, except that its hard. what you should do, is go to planetrenders.net and go to the 3D Abstract section. Thats what people use, most of the time i believe.
yes ive noticed they have some there and ive used them a few times but im still looking to make my own
o, ok, well go to planetrenders and sign in, then somewhere at the top(i dont know quite where), it says "How to render"... im not sure how to make designs, but it tells you how to make it a render... im not sure that helps you though... if it doesn't sorry, i dont know...
They can be made with any 3D graphics editor but most commonly Cinema 4D. They can be found in many places as well such as google images etc.