The weapons were allegedly picked up at different places: the rifle at the post office and the revolver at Railway Express. But there is no evidence of such pickup in either place by Oswald or anybody else.
It is not necessary to determine who picked them up but we can draw a reasonable inference that they were probably picked up by Oswald because:
1. He wrote the order - his handwriting was verified by Marina;
2. He carried photo ID in the name of the consignee A. Hidell;
3. He was in possession of guns that are indistinguishable from those shipped shortly after they were mailed (backyard pictures, Gen. Walker shooting admission, Marina identified rifle, etc.)