This stage is The Bullet Bill Express (3-Castle). This complete walkthrough will provide you with a 100% video playthrough and a screenshot of where you can find all the green stars. The green stars and the stamps for this stage are pretty easy to find, the key is to move fast to grab them.
Game Play Walkthrough Video
Green Star 1
You will see the star at the beginning of the stage, rush to grab it before the screen scrolls over.
Green Star 2
The second star sits on a stack of Goombas, kill them while watch out for the incoming bullet bills.
Green Star 3
Take the green pipe to transport to the other train in the background. Break a box to reveal a Toad who will reward you with a green star.
At the last pipe where the fire bros are, the stage stamp is located at the little room down below.
The boss will split into several persons and attack you with the shuriken. The key is to damage the real boss before she tosses the shurikens. The real one holds the pink ninja star. Wait at the center of the split so that you can rush to the real one quickly.