Supplier Access

I'm familiar with the adding an attribute on P2 of the items to control supplier access.

One case I do not know how to handle with roles and privileges is the following:

If an items is contracted to 2 suppliers and both have access to the item, how do I keep one from knowing about the other.

It does not make sense to me to have 2 numbers for the same item just to segregate suppliers.

Can this be done with roles and privileges, if yes please guide me thru setting this up?  If this is best handled with process please suggest that also.