you can get any Pokemon that you want.
you can trade
The only way to get a Deoxys in Pokemon Heart Gold is to either trade it from another Pokemon game that has it, or use an action replay code.
Through an action replay code
Use a action replay
There is none.
catching trainers Pokemon
No, there is not. Sorry...
insert the action replay than take it out and put heart gold in.
0000000b21000516450023263233434dsg00000123255524555455
Get an action replay from a game store.
go to necko seeker
use an action replay