The Strength up are found in several places in the game when you explore dungeons, The pearls are much rarer, you can get a pearl of strength from Coral in her rppm by bringing her a cowgirl milk and you can get a pearl of magic from her as well (you get to choose which each time) I know the pearl is +8 while the strength up is +5. I also picked up another 2 pearls but that was later at some point and you don't get to choose strength or magic. Hope that helps.
Sorry, I just read my post again, It should of course read "room" which is the middle of the three rooms at the bottom of the screen. You can't repeat it but I think you can take another pearl of stregth instead of magic - I took one of each, anyway I only have 2 of each in the game so far and I've played all the updates except the slave rebellion, I am postponing keeping two saves for as long as possible, hope that clears it up