Go to Staffleu and Cowan's TL2, which is available online and also in the jntbgri library.The names of collectors are arranged alphabetically and go the volume having the alphabet H for Helfer. May many authors are there in the same name, kindly get to know the full name of the author. From there you may get the details of herbarium specimens and its depositories. Then go to Various herbarium Catalogues online, and if not available online, write to the curators to send the images or cibachromes.