This is pretty urgent: does anyone know how to find out the original folders of files which are removed to Trash accidentally?
I'm afraid that you're out of luck. OS X does NOT keep track of where items in the Trash directory came from.
When Apple and Microsoft "borrowed" the idea of having a "safe delete" from Xerox PARC back in the olden days, Apple directly used Xerox's implementation while MS, having many extra months, added several very useful functions. It's too bad that Apple's corporate pride won't allow them to copy MS's Recycle Bin restore capabilities to their Trash.
Here's a trick that could have saved your butt, but it's too late now. But, hold it in reserve in the event that you ever do another accidental delete. (It would have been easier if Apple saw fit to ask for a confirmation before doing a delete.)
This will work only if the deletion was the last thing you did. Press command-Z which is the OS X UNDO command, just like ctrl-Z in Windows. This will return the deleted file to its original directory.
I've been told that OS X and Windows handle directory entries differently when files are "safe deleted", but I don't know that it's factual.
1) In OS X when a file is moved to the Trash, the pointer to it's parent is changed to the ~/.Trash folder. No record is kept of the previous parent.
2) In Windows when a file is moved to the Recycle Bin, a flag is set that tells Windows Explorer to display the file in a pseudo folder (Recycle Bin) instead of where it really resides.
