Where to get the hammer suit

According to this Super Mario Bros 3 Guide there are five locations in the game where you can obtain the Hammer Suit.

• Mushroom house two in world 6 gives you a hammer suit.
• World 6-10 has a hidden hammer suit in it.

Hit the second normal block above the white block and climb up the vine. Jump onto the platform, the last block contains a P-Switch. Once it’s hit you could jump to the right and collect some coins. Move quickly to the pipe covered in frozen Munchers. Melt them with fire and they will become coins. Go down the pipe to find a huge Question block holding a Hammer Suit.

• Mushroom house two and three in world 7 have a chance to drop a hammer suit along with a chance for a tanooki suit and frog suit.
• The last location is in world 7-8.

When you get to the second Ptooie go down the first pipe to discover a huge Question Block containing a Hammer Suit.