You can get Pokemon DarkCry by downloading it from Pokemonromhack.com but you should be aware of a couple of things before doing so.
Hacked versionPokemon DarkCry is not an official Pokemon release. It it a hacked version based on Pokemon FireRed.
As such, there are a number of inconsistencies within the game that have failed to have been addressed over the years. For example, Primplup is considered a water and ground type Pokemon in DarkCry, instead of just a water type.
There are also instances of offensive language included within Pokemon DarkCry due to the fact that it's not an official release, and therefore, it may not be suitable for younger players.
Risks of downloading
The other thing to consider is the risk of downloading files over the internet. Although websites may appear genuine, files sometimes contain nasty viruses and other rubbish you don't really want on your computer.
Here's a quick look at Pokemon DarkCry!