The OP appears to be based in Germany, so orbitz is of limited use (kayak is helpful for comparisons but ita is more effective IMO if you are just looking for fares rather than booking them).
To answer the original question, there are no alliance-based pricing website and I'd agree with Slawecki that the premise is problematic anyway.

For German-based fare search engines, the LH forum might be a better place to ask.