First off, friend codes are on user's profiles, so making a thread for it is unnecessary. Secondly, for pretty much anything regarding the 3DS, use [ahttp://dsipaint.com/forums/forum_thread.php?thread=8511]this[/a] thread.
It's my job to help the next generation, and set a good example for them. And for that I'll gladly lay down my life.
So here's what you do. Go to your settings and enter your 3DS code into 'Other Info'. Then ask around in chatrooms and on other profiles. And don't be too persistent because that can come off as annoying. Good luck.