Shikoku Nature Trail Resources
Traildino is a trail hiking database that offers some basic information about trail. It has a few of the GPS maps listed but it is very scant in this area. Provides overview of complete trail.
This a government website that breaks the trail section by section. You can navigate it by clicking the pictures of the section you want to see. It is one of the more comprehensive sites I have found. There are no topographical or GPS maps on this site. This site also has other hiking trails in Japan. For the Shikoku Nature Trail the Nature Lovers club also provides detailed brochures for this trail.
The Wikipedia page offers a detailed overview of the Shikoku Nature Trail.
There are no maps, or GPS information.
This trail is divided into four prefectures, and each prefecture provides their own maps. Depending on the prefecture they can be downloaded or they must be requested by mail. All links are in Japanese.