You won't be needing a Razor claw as Gligar only evolves with a Razor Fang.
You can find a Razor Fang at Route 13 and Abundant Shrine, you can buy one at the gear station. If you are wondering where you get the Razor Fang from Route 13, you can get it from a man that gives different item each day. He is outside the house with the move tutors that will teach starter Pokemon Frenzy Plant, Blast Burn and Hydro cannon.That house is also the house that teach Dragon-types Draco Meteor.
Hope this helps :).