Product restrictions in Order Entry

Hi everyone:

We are kicking around how to handle the following scenario, and I am looking for your input of how this could be best handled.

Item(s) cannot be sold to a Customer / Country based on item.  For example Acme Rocket Company can buy an item from us in the United States, but that same customer cannot buy the item in Japan from us.  We have approximately 47 different customers with 300 plus items that cannot be ordered in some combination where they are not allowed to order these.

We want the system to stop the order from allowing them to booking it onto an order.