In super mario 3, the locations of the warp whistles are as follows:
World 1 Level 3 - Duck down and hold it there on the Last White Block (this block is the centre of a cluster containing 4 other blocks) you can now rum Behind the Black "end of level" screen, you appear in a Toad house where the whistle awaits.
World 1 First Castle - on the first screen, get a Leaf Tail and fly Over the top, instead of going through the first door. a chest appears with a whistle inside.
World 2 - A Hammer Bros Level-ette: Keep all Rock Hammers you get at Toad's, use a hammer in the Top corner of the map on the very far right, fight the hammer bros (these dudes spit fireballs) for a chest with a whistle.
Whistle-Accessible worlds are:
2,3,4
5,6,7
8,
if you want to repeat some worlds, for points or booty (world 6 has hammer throwing suits for example) then be sure to do it in that world. However, if you are on world 4, you jump to 5,6,7. if you are in 7, you jump to 8. and 8 is boring lol