The Wishbone also works in the Swamp Biome, there are Iron deposits on the surface you can find. Just have to worry about the odd mob coming to harass you.

I find that the benefit from Silver armor isn't that much better than Iron, so I usually fully upgrade my Iron and completely skip Silver. Once you hit the Plains and start getting Flax to make thread, Silver becomes obsolete and you'll need lots of Iron from the Swamps again to make Padded armor.