There is no way to get the uri of the found feeds, this patch adds that functionality:

Index: library/Zend/Feed.php
===================================================================
--- library/Zend/Feed.php       (Revision 14152)
+++ library/Zend/Feed.php       (Arbeitskopie)
@@ -355,7 +355,7 @@
                 } catch (Exception $e) {
                     continue;
                 }
-                $feeds[] = $feed;
+                $feeds[$uri->getUri()] = $feed;
             }
         }

I'm not sure if such a change is possible - if not another solution would be nice.