The species in the Trophy Garden on a particular day is picked at random from a list of 17, so you could just try once a day until it shows up.
I have heard that if you save before talking to him, and reset your game if he mentions a species you are not interested in, you can get a different one, so that might speed things up a bit.
u can get after u get national pokedex at mr. backlots trophy garden
In the Trophy Garden.
in the trophy garden
In the Trophy Garden
trophy garden
The Pickachu in Pokemone Platinum is in the Trophy Garden.
Trophy Garden.
trophy garden
They are found in the trophy garden.
Trophy Garden
trophy garden? i forgot
the throphy garden is south of hearthome city