I DESPERATELY NEED IT FOR MY BLAZIKEN!!!
You can buy choice band in battle frontier in emerald with BP. However, you can't get choice specs/scarf since it was made in gen4
http://bulbapedia.bulbagarden.net/wiki/In-battle_effect_item
You can buy Choice Band with BP in Platinum Version, and I think Pearl and Diamond too. And you can get the item from your Mom in HeartGold and SoulSilver. Sometimes she buys it for you.