Le problème de indexToItemRenderer est qu’il ne retourne que les items visibles. Pour accéder à tous les rendrerers d’un objet,  il faut adresser mx_internal::rendererArray , voici un exemple tiré de :

http://cookbooks.adobe.com/post_Flex_3_Looping_over_itemRenderers_in_a_List-10403.html

package Controls
{
    import mx.controls.List;
    import mx.core.mx_internal; //this import statement should appear be last

    public class ExposedRendererList extends List
    {
        use namespace mx_internal; //tells Actionscript that mx_internal is a namespace 

        public function ExposedRendererList()
        {
            super();
        }

        //The array of renderers being used in this list
        public function get renderers():Array
        {
            //prefix the internal property name with its namespace
            return mx_internal::rendererArray;
        }

    }
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, “Courier New”, courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }