i think so but im not 100% sure
In the grassy areas
It is exactly where you described it. It's on route 9. If you mean specifically how to get the Pokemon, you need to go into a grassy area, cave, or other place where wild Pokemon appear on that route to find the swarm Pokemon.
They don't just "appear". You have to look through grassy areas for wild pokemon. In Ruby/Sapphire they are common on Routes 110, 117, 119, 120, 121 and 123. You can also find them in the Safari Zone.
The grassy areas where you start out.
you get a Pokemon that knows sweet scent and use it in a grassy patch
unless they are in grassy patches you cant, only with action Replay or R4, (i dont even know why they make shiny legendaries if they are so hard to come by...)
You need to have the pokeradar. When you use it in a grassy area, some of the patches of grass will move. Every time you walk into the patches, a Pokemon will appear. Every time you defeat or catch that Pokemon, it will trigger new patches to move. The patch furthest from you will contain the same Pokemon as before, and the more times you see that Pokemon by using this technique, the more likely it is for it to eventually appear shiny.
route 201 route 201
You have to choose charmander as you starter. Then you will find it at random on mainland (not islands) grassy areas.
Use your pokefinder and walk to make sure it is charged up. Go into a grassy area and use the pokefinder and places with pokemon will shake. If it shakes and sparkles then its a shiny. it takes a long time but garentee it works... :)
Wild ditto can be found in the grassy part of the giant chasm
In the rocky area or the grassy area,hope i helped