ice
There is no other place to get it besides Mount. Coronet. Sorry
Dragon Pokemon are effective against other Dragon Pokemon.
Dragon type moves are only super-effective against other dragon Pokemon. However, if the dragon type move is on a dragon-type Pokemon, the move will do substantial damage to many different Pokemon. This is because, dragon-type Pokemon usually have outstanding stats which make them stronger than other Pokemon.
Dragon-type moves are only super effective on other Dragons. However, they usually have high stats and can learn attacks of any type (depending of the Pokémon) either by leveling up or by TM's or HM's.
Giratina(Ghost & Dragon)
Yes you can get other Pokemon that arent in pearl.
You can get it by wild Pokemon such as seahorse (not always) and any other dragon type Pokemon.
Only other Dragon types.
A pure dragon Pokemon is only super-effective against other dragon Pokemon. However, due to their insane stats most dragon Pokemon can take on all of the other types. Just as a reminder, dragon Pokemon are weak to ice and dragon type moves, and resistant to electric, fire, grass, and water type moves. This answer only applies to pure dragon Pokemon. Extra types such as flying/dragon, will have more weaknesses and strengths.
A pure dragon Pokemon is only super-effective against other dragon Pokemon. However, due to their insane stats most dragon Pokemon can take on all of the other types. Just as a reminder, dragon Pokemon are weak to ice and dragon type moves, and resistant to electric, fire, grass, and water type moves. (This answer only applies to pure dragon Pokemon. Extra types such as flying/dragon, will have more weaknesses and strengths)
dragon and ice is most efective against dragon.
Other gladiators.