A hint but not walkthrough for people playing majoras mask. it’s the earliest you can get the masks but not where to get them.

(does not include deku, goron, zora and fierce diety)

You can get six masks before even leaving the town once you get human again. (kafei mask, fairy mask, birb mask, keaton mask, postmans hat and bomb mask.)

in termina field you can get the dancing mask

After beating woodfall you can get the mask of scents and mask of truth

Before you enter snowhead temple, you can get the frog mask

here are some masks you can get after getting the zoras mask before the water temple:

all nights mask
bunny hood
lovers mask
crying luigi mask
romani mask
garo mask

Between beating the water temple and entering the stone tower temple you get two masks

the last mask is in the last dungeon.