Any store as long as you have one gym badge
Usually ultra balls are sold in the later cities try blackthorn city or the Pokemon league.
Buy an action replay from gamestop
You buy them at the Safari Zone, the shop right in front of the Pokemon Center (the girl with next to the Butterfree). Along with Quick Balls, she also sells Dusk and Nest balls.
You can buy them at the Pokemon mart at the Pokemon league. I buy my timer balls, heal balls, etc. at the Pokemon mart in canalave city
On the 2nd floor of Goldenrod Department store :P
From what I know, You can't BUY master balls in Pokemon.
I do belive there won't be that kind of cheat, but a smart, but long way is to buy a Pokemon pearl, or diamond, then cheating on that game, then trading and having those Pokemon have master balls.
you cant buy master balls in any Pokemon game so far. you only get one from prof. elm afta you have got all 8 johto badges
U can't buy fast balls but u can buy quick balls or maybe get them out of apricorns
You can get them from the lottory or Professer Elm but you can not buy master balls.
No you can't buy cherish balls in pokemon. You have to get them in a wi fi event.
Use your strongest Pokemon, do not attack, buy 15 Ultra Balls, 5 Great Balls, 20 Poke Balls, and 6 Timer Balls. Keep using the balls, save 5 of the Ultra Balls then use a few Timer Balls. They are guaranteed to catch Deoxys.