you find him in eternea city near the bike road in a small house.
Sandgem Town
he's up prof. rowans butt
firstl u dont hav a boyfriend u hav a rival and prof rowans assistant ur rival is at the fight area when u hav beeten da elite 4
Well you have to train it to at least lvl70 oh and go into prof rowans lab
"Your next destination is Hearthome City, which is due south of Eterna City via the Cycling Road. On the way out of town youll run into on of Prof. Rowans assistants, who will check your progerss and reward your continued efforts with the Exp. Share item (if you've seen 35 or more pokemon)." - Page 65 of Pokemon Pearl/Diamond Guide. So, go to Eterna City, and go down and through the Building at the bottom of the city (leads to Route 206), and if Prof. Rowans Assistant doesnt give you it, then im not sure. Im just showing what the guide says.
He's not in pearl version.
Prof rowan is only in diamond and pearl and platinum.
all you have to do is see every Pokemon in the sinoh dex then you go to prof rowans lab and he will give you your national dex
he gives it to you in prof. rowans lab. for this you have to complete sinnoh pokedex(excluding event pokemon).
beat the elite 4 then go to rowans lab in sandegm town and prof oak will come and upgrade your sinnoh dex into a natonal dex
Well you Must find all Pokemon in Sinnoh. Then go to prof rowans lab in sandgem and he will give it to you o and if he doesn't then that means you didn't talk to your friend that was outside of the lab ( in sandgem where prof rowen is)he will to you to go some where and the place where he tells you to go is where the old lady will show you Pelkia or Dialga matters what game you have and ya that's it.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!^_^ =]
You get it from Prof. Rowan after you get the national pokedex.