That being said, there's also an even simpler way if you're not all that crafty.
During the run of The Wolverine in theaters, Hasbro released Nerf claws. For 10.99 USD - 12.99 USD, depending on where you buy them, you can have a great basis to start for a quick set of X-23 claws.
Now that's just a start mind you. Once you have two sets of these claws, all it takes is a pair of scissors to make a little correction to them.
This method, as you can see, gives you an extra claw to use too. This one you can affix to socks inbetween the big toe and the next, or if you feel more ambitious, you could also attach it to a pair of shoes. Both methods give you X-23's foot claw.
The handle version of the normal claws are ready to go once you clip the middle claw, but if you feel more adventurous, you can also attempt sewing it into a pair of gloves or sleeves for a more inbetween the fingers look. I'm sticking with just the handle version as these are undecided as to who will use them for a photo shoot as yet. They were created on a random what if thought... So we'll see if they ever get used.
So there you go. Now you have a pair of X-23 Nerf Claws, plus a foot claw to use as you see fit.