It is impossible to manage future order book and stock allocation. Please add product availability to the sales quotes report.
I've found a work around which is to download the inventory, and populate the product additional attributes 1/2/3/4 with on hand/available/on order/allocated values and re-upload as daily manual batch task.
Then, when you run a sales quote report it gives you some idea if you enough on hand and enough on order, when you group the quote report by product, but obviously it gives no dates. The 'On Order' PO quantity might be 6 months away, but it's a start.