Repeat ball will be sold at a shop on island two after you beat the elite four
yes you can!
somewhere in the game
Master Ball
After completing the sapphire and ruby quest and beating the elite four for a second time head to two island and talk to the guy who runs the mart, he will sell you timer balls and repeat balls and more.
Only one
use a master ball on it
Have a friend trade you a Pokemon holding the master ball they received.
you cant. the trainer will block the ball.
u cant
There is only one
No unless you have a game shark
you use a ultra ball