Trade
You can get growlith at route 201 and 202 if you have Pokemon firered insterted.
mostly: evee------flareon vulpix-----ninetails growlith---arcanine
u have to w8 for a migration to come or get an action replay then get the Pokemon modifier and pokedex cheats.
Growlith can be found in route 37.
You have to have Pokemon fire red for GBA. Catch it on that.Once you have beaten the elite four and finished the Sinnoh Dex (on diamond) the Pal Park will open and you can migrate it from fire red to diamond.
Im afraid there is no other way except using an action replay cheat cartridge.
You can catch a Growlith in the Pokemon Mansion on Cinnabar Island.
you should train growlith until it learns flame wheel, then evolve it.
I'd say Mareep, Totadile, Machop, and Growlith.
Growlith Issac Lim
You can't get Growlithes in Pokemon diamond :( But if you have firered or leafgreen then you can trade via pal park to your Pokemon diamond game. I got a Growlith in Pokemon dimend! (With out a cheat!) I was just woundering on root 202 going to Jubilfe city because I had to do something! (I realy don't remember!) Oh! I allso got him AFTER i beat the game!