Where can I find swords from the other games?

Prince sword: Step on the lone scarab.
Location: The lone scarab is after the first time you have to run away from them. Just after you flushed them away go back down and just outside the round chamer you're is is the scarab.

King sword: Touch the red crystal.
Location: in the room between the second and third encounter with the giant creature you're chasing through the first half of the game. It's easiest to reach when you have the magical spheres.

Sand Dagger: Launch yourself from the cannon.
Location: it's in the very first room of the underwater palace after the Gems puzzle. There's a pipe sticking out of the wall very low to the ground on the right as you enter. It's in the area with all the red stuff that kills you. Find a way to get in that pipe using your sand sphere.

Wall breaker: Find the monolith.
Location: Challenge of Humility(space area), underneath the bull's head.

No credit to me, just good searching on the internet:P