Of immense benefit while writing the saga has been The Atlas of Ancient and Classic Geography
by Samuel Butler, available online from Project Gutenberg. This was particularly useful for understanding the country around Iolcos and Mount Pelion; for identifying the route travelled by Cheiron, Jason, Peleus, Telamon and Heracles; for identifying the kingdoms visited by Jason and Peleus and creating a route for their embassies; and for identifying the route of the Argonaut expedition itself.
The online edition can be found here
Also of use was Maps of Ancient Greece
by N.S. Gill.