You can only get Snorlax by evolving Munchlax.
Iron Island.
You can get Houndoom in Pokemon Platinum by evolving Houndour. Houndour can be found on Route 214 and Valor Lakefront! Houndour will evolve into Houndoom at level 24.
You can get Ampharos by evolving Flappy which you can get at route 222 (with Pokeradar) but it's uncommon.
The evolution stones in Diamond/Pearl/Platinum are the water stone, fire stone, thunder stone, moon stone, leaf stone, sun stone, dusk stone, shiny stone, and dawn stone. (Sorry if I missed one) And even though this is the opposite answer, the stone to keep Pokemon from evolving (with or without evolution stones) is the everstone. Hope this helps! :)
You can only get Snorlax by evolving Munchlax.
Most evolving stones can be dug up from the underground tunnels. I'm not sure where to find them in the game. I do know though that you can find a thunderstone at fuego ironworks.
You can find stones undergrounds.
You cannot catch a tiranitar on any pokemon game, you have to get him from evolving Pupitar.
There are two ways to evelove Pokemon in Pokemon platinum by lefstones and leveling up.
The Underground
there is none sorry
Iron Island.
Togetic into Togekiss and Roselia into Roserade
You can get Houndoom in Pokemon Platinum by evolving Houndour. Houndour can be found on Route 214 and Valor Lakefront! Houndour will evolve into Houndoom at level 24.
Flying stones are like master balls except for evolving Pokemon, you can use it on any Pokemon instead of leveling, other stones, friendship ect. Pokemon like tyrogue will still evolve depending on their stats. The most widely used method for flying stones is evolving a phione to a manaphy.
There is a store at the end of the game where you can buy different stones for evolving.