First of all you have to encounter the galactic grunt in Pastoria city. When you follow him all the way to Lake Valor you will then see Cynthia with a secretpotion. The secretpotion will then allow you to move the group of psyducks in route 210 which will allow you into the foggy area
You can't get altaria but you can get swablu at the top of route 210 where it gets foggy.
According to the Sinnoh Dex numbering system the Pokemon that is number 29 is Golbat and you can find it with a Ninja Boy in the foggy area of Route 210 in Diamond and Pearl.
You evolve it from a bagon to a shellgon to a salamence. (P.S Bagon can be found on Route 210 in the foggy area).
A Trainer between Celestic Town and Solaceon Town route 210 has one.
all the Pokemon on route 210 in Pokemon diamond and pearl are ponyta, geodude and if your really lucky you can find onix.
use pokeradar on route 210
Ace Trainer At Route 210
No where but in PEARL you can catch a BAGON route 210 with a pokeradar.
Milktank is located in route 209 and 210 in both Diamond and Pearl.
you can catch one at north part of route 210
Route 206 , 210 , 211 , 214 , 215
Route 210 (fog) you have to use the poke rader to find it.