Originally posted by That guy with the Spoon:

i guess a lot of mistland biomes are bordering plains so farm some and smelt it there?

I suppose the good news is that the Ancient Armor or Weapons that are mineable in Mistlands drop Scrap Iron that you can smelt to make the Blast Furnace. Iron Bars seem to be scavenge-able from some of the structures in Mistlands as well.