you can not get it from Pokemon platinum you can trade in to diamond or pearl
It learns it at Lv61 in Platinum.
you can find a grip claw in 217 because there are sneasel that are holding grip claw
Route 244
On Victory Road's first floor
get a razor claw and a sneasel and level up
After you beat fantina at the gym in hearthome city she will give you the TM shadow claw.
If you want to get quick claw in D/P or Platinum you will have to get it from R/S/E and migrate a Pokemon holding it
its gone u dont get another
In the low right corner of Route 24.
Use a Pokemon with mean look, or use a Pokemon with a trap ability.
No wild Pokemon hold the item razor claw but you can find razor claw at Route 224, Victory Road and available to buy at the Battle Tower (D/P) -Clensen