In order to get the source of a specific page, you can follow one of the two methods described below:
Segmentation:
1) Select your site and the period
2) Create a visit-based segment and select your page from the "entry page" dimension
3) Apply your segment to the Sources > Sources > Sources analysis
Filter:
1) Select your site and the period
2) From the Navigation > Pages > Entry page analysis, apply a filter to find your page
3) Click left on the page label and select "Traffic sources"