This was the only "draw 200 of X" that didn't unlock naturally during my first run through (i died quite a bit) so I loaded up chapter 5-2 (chamber of fire) as there's a fireball right near the start of the level and it only took less than a minute to get the 20-30 i needed. But if u just want to boost this, the first chance you get is right at the end of chapter 5-1 (getting warmer)