It depends on the Pokemon you're trying to evolve. While some Pokemon can evolve without any problems due to being in the regional Pokedex, other Pokemon (Golbat, for instance) won't evolve without the National Pokedex. Note that this is only the case in FireRed and LeafGreen - in later games, Pokemon not in the regional Pokedex will evolve, but won't be recorded until you get the National Pokedex.
You can trade, use the action replay for Pokemon Platinum, or actually catch it without the action replay. If you have completed the Sinnoh Pokedex, go and see Professor Rowan, and he will give you the National Pokedex, then you catch all the Pokemon throughout the land of Sinnoh from all the other regions due to an "outbreak". But, where to catch caterpie specifically, you need to go to Eterna Forest, west of Eterna City.
you cannot get manaphy without action replay if you go to the Pokemon mansion with the garden theres a book you can read that will add it to your pokedex
The Trophy Garden is the only place to get Ditto in Pokemon Platinum, without trading or cheating of course.
There are only two Pokemon(without the National Pokedex).They are Pickachu (into Raichu) and Eevee (into Jolteon).
you cant
You must have the National PokeDex to capture Heatran.
eterna forest 10%
You can catch them on Iron Island once you have the National Pokedex. You get this by seeing all the Pokemon on the Sinnoh Pokedex.
u hav to find all of the Pokemon in the national pokedex
It depends on the Pokemon you're trying to evolve. While some Pokemon can evolve without any problems due to being in the regional Pokedex, other Pokemon (Golbat, for instance) won't evolve without the National Pokedex. Note that this is only the case in FireRed and LeafGreen - in later games, Pokemon not in the regional Pokedex will evolve, but won't be recorded until you get the National Pokedex.
you have to trade them from a game that has the national dex.
No, not without action replay or hacking unfortunately. I hate to say it, but sorry. There were wi-fi events but you missed them.
no
there was a code to fill in missing numbers for the pke dex but it would completely mess up your game.
you have to get it in Pokemon platinum version and then trade it into soul silver or heart gold. you have to do the wi-fi event to get shaymon though.
you need a cheat for it.