Hi Justin,
First for find the Sales Order no, go to table LIPS enter the delivery no and then get the value of field VGBEL. this will give you the Sales Order number as shown below.
Now copy these sales order numbers and enter them in table VBPA along with partner function as PY or RG(german). you will get the corresponding payer as below:
For corresponding purchase order no, go to table VBFA enter the sales order no and in subsequent document category "V" i.e Purchase order and execute.
you will get the PO number as well. (i havev used a different Sales order in this case to show you how to find it)
Either you can run these steps manually each time or it would be much better if you get an ABAPer to right a simple report for this logic i explained. will hardly be 1 hour work.
Regards,
Aayush Jain
SAP SD Consultant