Is there any library/source or database through which we can search that the new compounds identified by GCMS in a specific plant is already been discovered in other plant or microorganism?
Essentially all chemicals (synthetic and natural origin) receive a CAS Registry Number. In this case, these compounds can be considered as "known". With this number, you can make database searches, in which natural sources this compound has been identified already. One of the largest databases is the Chemical Abstracts Service with their Scifinder software, a commercial product of the American Chemical Society.