You can buy it in mistralton city at the pokemart for $50,000
Route 212 http://bulbapedia.bulbagarden.net/wiki/TM11
it is on route 120
Route 212
A copy of TM11 can be found on Route 212 in Pokemon Pearl. In addition to the one found in Route 212 there's a NPC who you can trade colored shards for different TMs with TM11 being one of them.
In Pokemon Pearl TM 11 can be found on Route 212. There is also a NPC in route 212 who you can give 10 Red Shards to receive another copy of TM11.
TM11 Sunny Day can be found in the Safari Zone.
Go to the 3 Floor in the radio tower next to and she will give you Sunny Day TM11 and then go catch HO-OH
TM11(Sunny Day) TM35(Flamethrower) TM38(Fire Blast) TM50(Overheat)
There is nothing there other than a single item, TM11 (Sunny Day). The Scorched Slab represents Japanese Mythology, where Amaterasu the Sun God is said to be sealed. It is more of an Easter egg than an actual location.
Actually, there are no Pokemon at all in The Scorched Slab. Just TM11. It is at the top and route 120, in the water. (Surf on the first pond on route 120 from Fortree.) All you need to get there is HM04 (Surf).
You can find Sunny day (TM11) in Scorched Slab, this is a small cave found in Hoenn. It can be accessed by surfing in the north of Rout 120, next to Fortree City, in a indented lake.
Pokemon black pokes pokemon if weathered otherwise pokes black