Go through your script and list all the metal props needed. Then, go through the script a second time with your list to make sure you didn't skip anything.
Assess your list to see what you need to make. You want to make metal props that you either can't borrow or that would be too heavy or dangerous for your actors.
Make swords and other metal weaponry out of wood. You can either purchase these or have your scene shop cut them for you. Cover them with metallic silver duct tape or metallic paint. Swords made of wood look more realistic than cardboard or foam when actors swing them.
Carve foam to resemble more complex metal stage props that require more detail. You can cut a helmet out of polystyrene and then use metallic paints to give the helmet the metallic sheen you need.
Use metallic fabrics to cover large surfaces. Create a metal wall by covering a flat with metallic fabric.
Cut metallic card stock to create jewelery and other detailed, expensive-looking stage props, like crowns. Or, cut regular cardboard and cover it with metallic duct tape or metallic paint.