You can use the Cold Casting method to turn your 3D Printed objects into Metal Show Pieces
Once you have the 3d printed model you want to turn into metal in this method the first step is to print the item on your 3D printer. Then you will make a silicon mold of the 3d printed item. The next step is to do the casting with resin and your preferred metal like iron or bronze. Once it is dry remove the silicon mold and you have your metal item. Now you can give it some shine with fine steel wool or similar. If you prefer you can even give it a rusted older feel.
I found this video detailing the exact process to do this step by step. He seems to make it look so easy.