@jon.correa you can do that several way, one I could think quickly would be having a custom fields(list/record type) where you can reference the originating SO, then you can create a transaction saved search for PO(criteria) with that reference field, also make sure to set the originating SO as filter --> save it as sublist --> create custom sublist and apply to SO --> select the previously created saved search and save. Now SO will have that new sublist showing related PO's - and since you have originating SO as filter it will only show PO's that have reference to the SO.