Welcome to PokéBeach! ☺
You can find the VG trade threads here
http://www.pokebeach.com/forums/forum-wi-fi-zone.
You can also start your own trade thread.
Enjoy!
LLR
PS
You don't use the GTS when trading with friends.
You use the "Trade" on the PSS screen. (That's the screen that shows passerbys and friends online. )
You both have to add each other to your friend lists.