Moving between combinations

[CJH]

I wonder if there is any solution here ...

I have a shop in 1.7.7.0. Products are always priced including postage, which means that combinations are based on the post destination so that the price changes accordingly. But when there is a single product available (say, a used book), it can only be assigned to a single combination and the others show out of stock.

Is there any way, or a module perhaps, that will look at the number of products available and show these against all combinations, but not permit more than are available to actually be sold? Example: 1 book exists, with three possible prices/post destinations. It has to be assigned to one, but it needs to show as available to all three to allow other destinations to buy it. But, once sold all three must show no stock.

If that made sense, is there any way of achieving this?