How to get the control of ribbon xml outlook add in c#

I need help in outlook add in. i have added a ribbon.xml page and added the combo box in that.
    "<comboBox id="cmb" onChange="change" getLabel="Data"/>"
Now i need to add items in that during run time. i thought i will add in Ribbon_load but i could not get the control there.
          
        public void Ribbon_Load(Office.IRibbonUI ribbonUI)
                {
                    this.ribbon = ribbonUI;
                       
                 }
 here i am not getting the control "cmb". is there any other way to get the control.