My friend group had basically just finished a run when Mistlands came out (All we had left to do was beat Yagluth, so it worked out perfectly).

Since it was an old-gen map, we had to pass 3 island-y mistlands before we finally found a real mistlands biome, 5 infested mines so far and at least a dozen dwarf settlements!. I definitely recommend just putting in a bit more time exploring - it's faster than starting from scratch, that's for sure.