Normally someone would run MRP via Planning Worksheet to generate suggesting purchases. There are a number of reports in the planning area that might work - but I have no idea what MD4C from SAP is and I'd be surprised if there were more than 1 or 2 people on this forum who do.
When you say "PO's are missing for each production order" that is a bit confusing. Production Orders assume that material will be drawn from inventory and it's unusual to peg Supply to the Prod. Order Demand.
What kind of projects are you doing that you match POs to Prod Orders?