You can search the content by the source. Typically, that's available in the wire text and image searches, and allows to narrow results to only selected feeds.
In Ted4 and Fred4
On the search pane, click the Source field, and then select one or more sources:
Click the refresh button, if necessary, to display the results.
In Browser
On the search pane, click the Source field, select In, and then select one or more sources: