I'm going to be in a ninja

if you pause at around 0:16 you can see basically what it's supposed to look like. But not EXACTLY like that, just in case you didn't know what I was talking about.
So far: The entire assembly is going to be mounted to a shinguard, with a narrow steel plate attached to it (lengthwise) to provide a base for the blade. a Keyring is going to be put around my middle finger, attached to the trigger. When I pull up on the keyring, it will pull up on clothesline with a pin through it going through a hole in the blade at the bottom. A cord tied to the back of the blade will be how I will pull it back in. The blade itself will be covered by a half of a PVC pipe cut down the middle, and I will put the trigger on top. The spring will be put at the bottom, kept in by the PVC pipe.
I know how I'm going to put the spring in, I just need a way of putting the blade on a track or stabilizing bit of sorts to keep it from wobbling around while it's not deployed. And a way of cleanly stopping it at the end to prevent it from flying off.
If anyone has any better ideas, go ahead. And yes I have seen the indiemogul video about the quick-deploy gun prop thing, and it seems waaay too bulky/expensive/heavy for my purposes.
And no this is not some stupid inane fanboy daydreaming, I want this for my friend because he doesn't have anything in his ninja arsenal and he's making the smoke bombs. So there. (and if this is in the wrong forum let me know...)