Find the answer to your question
There is a new tag QuantityAvailableHint field in the GetItem call that indicates the type of message that will be returned describing the quantity available for the item. Can I specify it in Add/Revise/Relist calls?
QuantityAvailableHint field is available only for GetItem and GetSellerList calls. You can set it by going to the Sell Your Item form and listings in Home > My eBay > My Account > Site Preferences Page as showing below: