I do not know where you can find volume III at the Internet but you can find these books as photoreprints:
Meyers Orts- und Verkehrs-Lexikon
des Deutschen Reichs
Raymond S. Wright III
( Appendix to Volume II (originally published as part of Volume II ), Leipzig 1913.
Volume III:
Supplement published September 1913.
Reprint together as Volume II of Meyers
Orts- und Verkehrs-Lexikon des Deutschen Reichs
by Genealogical Publishing Co., Inc.Baltimore,
Maryland 2000.
Printed in America.
Library of Congress Catalogue Card Number 99-85938
ISBN 0-8063-1631-4 (set)
ISBN 0-8063-1637-3 (Volume III)
Hope this will help?
Wilhelm