Bill of Materials with both internally and externally sourced components

 Does anyone know how to successfully create a bill of materials with at least one internally sourced component (after booking, line would pick release and then be available for picking/shipping) and at least on externally sourced component (after booking, line would purchase release and create a requistion)?

We have a need to do this as we are sending materials to a 3rd party, who creates the finished product, which we then sell to our customers.

We are maintaining in our inventory the count of the materials that are sent to the supplier. We need to relieve the quantity of the material when the finished good is sent to the customer.