Search by Model, for example "ag-dvx100a". The page displayed will list all the part numbers. I don't recall the exact part number of the mic holder. Your manual contains a diagram with the part number.
I busted mine and ordered one through the site. Got it quickly.
Be careful, it is a combination of two separate parts, one is the elbow joint, and the other is the actual holder, and depending on where yours broke/lost, you may need both. Usually $70 for both.