How do you get to the frontier brains in Pokemon platinum?

Answer 1

It is very simple. Challenge each battle frontier building and win three times in a row and on the 7th battle on your third challenge someone will tell you that the frontier brain of that facility will want to challenge you. ( You have no choice but to battle them)

Answer 2

For the Battle Tower Frontier Brain named Palmer, you need to have a streak of 21 consecutive wins in order to battle him.

For the Battle Hall Frontier Brain named Argenta, you need to have a consecutive streak of 50 wins in order to battle her.

For the Battle Factory Frontier Brain named Thorton, you need to have a streak of 21 wins in order to battle him.

For the Battle Castle Frontier Brain named Darach, you'll need to have a consecutive streak of 21 wins.

For the Battle Arcade Frontier Brain named Dahlia, you need to have a consecutive streak of 21 wins.