Most of the small expensive bags contain artificially colored gravel anyway. I don't know how something like this looks after 5-10 years of outdoor use...

I suppose you're just searching for different kinds of rock? If so, the keyword is "Naturstein". Here are some yellow pages for you, and a section of organised producers.

The stuff from this company isn't cheap either but at least not everything is stuffed in small bags and they'll make better prices for large quantities... "Discover numerous kinds of split and gravel, ranging from white, beige, green, grey, brown, to pink, yellow and black" - Sounds promising? Or search for natursteine in Germany... Good luck!