You can use any Pokemon that is able to learn Strength to push rocks.
strength
have it hold king's rock them trade it to another Pokemon platinum..
you can get a rock climb TM (i forget where) and teach it to an able pokemon.
By using the move strength.
http://www.serebii.net/platinum/tornworld.shtml
all the beginners can learn rock climb
To catch garintina
dep
from the foreign guy
In Eterna Forest.
use strength
The HM Rock climb is on route 217.