I don't suppose there's anything wrong with the use of the Present Perfect in the question "Where have you found it?", is there?
It refers to the act of finding, not to the fact that it is presently found. The 'finding' occurred at a specific time and place in the past.
But there are a lot of contexts where the present perfect would be right, such as:
Have you found it yet?
The lost diamonds have finally been found. BUT Where were they found? NOT Where have they been found?