You can buy styrofoam pumpkins at the dollar store. Then just spray paint them silver–outside is best to minimize fumes. Use an old cardboard box as your spray guard. Cut off the top and one side so that you can spray the pumpkin without getting excess paint over everything. Just a hint: wear old clothes!
This idea comes from DollarStoreCrafts. Click the title for a link to a picture of their display of the silvery pumpkins. You could do more of a light dusting of the silver if you wanted to for a kind of “frost on the pumpkin” look. These silvered pumpkins work from fall into all the winter holidays. You can add a dusting of clear glitter if you want to get really glamourous. You can give the same treatment to pinecones, dried gourds, dried weeds, old wreaths, nuts, old decorations, & various ornaments/decor items. I love an arrangement of these types of items as a holiday centerpiece or mantle decoration. Gorgeous!