Spoiler: show

level 6 is opposite of first quest's level 9. (in the other rock)
level 7 is close to the start, a whistle secret. (a few screens east)
level 8 is under a bush one screen north of lost woods.
I won't spoil the location of level 9 other than its about where you'd expect a level 9 to be.
There are two old bomb men, one in level 2, and one in level 6