My WGR5 has a map titled Lands of Iuz. Checked the serial number and it definetely belongs to WGR5.
If you're in for the playing info too and not the collectables only, check out the erratta maps available for WGR3. Also there's the great WGR7 Ivid the Undying which was never published but available for download. Check the erratta/downloads section of the main acaeum site.
Other maps and more Greyhawk goodies are available on
canonfire.