I'm not sure if there are any direct files in the armory, but I know there are a few videos out there of people making these types of arms, and I'm sure you have already seen the cat cosplay, maybe you can try and get in contact with her and see how she did it. You will probably have to free hand it using polystyrene, but I know cosplay Chris has made a similar idea in his "mr whippey" cosplay so maybe you can watch his video and get an idea