To clarify rckoenes answer:
Unless you are the original manufacturer of an accessory that contains an authentication chip, you most likely will not have the correct credentials to use from your code.
Apple provides external SDK accessories to manufacturers so they can develop their products. They do not provide it to third parties for the development of software for other third-party products.
The only way you can successfully communicate with the accessory using bluetooth is to have the correct authentication keys and external SDK. If you do not notice it, you cannot do it.
GameKit is a more general way to use bluetooth, but it will not work for external accessories.
The only thing I can think of is a jailbreak of the phone, etc., but I am not ready to help with this.