The Shamadan is a very special prop, strictly for advanced belly dancers - not only because it's an extraordinarily heavy thing to balance on your head, but because there's fire involved! It's traditionally worn in the zeffah (Egyptian wedding procession).
Look for a style with large saucers under the candleholders, to catch the wax (otherwise your costume will be covered in the stuff!).
Shemadan on eBay
Note: It's rare to be able to buy a shamadan and wear it straight out of the box. These are not precision-engineered items! You may need to bend or adjust the arms to get the balance right, improve the padding and adjust the size of the headband.
Featured shamadan available from Bellydance.com