Handle annotation layers with arcpy

ArcPy does not expose all of ArcObjects. From what I can tell, this is one of the many interfaces that are not exposed in ArcPy. Only Page Layout elements are exposed in arcpy: ListLayoutElements (arcpy.mapping)

If you need to do this your only choice is ArcObjects. If you want to use Python, see How do I access ArcObjects from Python?

Otherwise you might want to look for or create an ArcGIS Idea about this (the only relevant existing idea I found was this one).