Hi, welcome! You see, in black version the only pokemon you can find in the wild are the newest, generation 5 pokemon, UNTIL you have beaten the game (ie the elite four and champion). Then in the new areas you will be able to find some older pokemon, as well as outbreaks in any areas. As for wifi, if you are talking about the standard GTS (not negotiations), then yes, it only lets you search for pokemon you have registered on your pokedex, either by catching or just seeing in a battle. However, if you go to GTS negotiations you might be able to find someone offering an older pokemon or one you haven't seen yet. Or, you could try to find such a trade partner in this forum under the gen 5 trading section! And one last thing, don't call the pokemon "monsters"...yes technically they are "pocket monsters", but MOST people who are fans of the series, at least in America, don't use that term. Just saying :-).
I'm sorta back
While I'd always love to talk about anything pokemon, I will only be using the 6th gen Wifi section for a while out of efficiency in my life, unfortunately
My 3DS friend code is 0576 3520 6954