On windows vcards are saved by default in the user directory "contacts". There is a command line utility to merge vcards into a single file.

   Combining files using windows copy at the commandline:
   To combine files, specify a single file for the destination, but multiple files as the source. To specify more 
   than one file use wildcards or list the files with a + in between each (file1+file2+file3)
   When copying multiple files in this way the first file must exist or else the copy will fail, a workaround for
   this is COPY null + file1 + file2 dest1
  
copy /B *.vcf all_in_one.vcf