Many garden supply places carry this. and you can buy it by the foot there.
You want the 3/4" ID hose for paintballs.
You can feed balls through a 5" radius curve. Good stuff for remote ball feeds for tank markers etc.
Here is the link to an internet vendor:
Here is a picture of the product: $19 for 25 foot plus shipping etc.
They conveniently fit many hopper feeds and you can union it using a piece of 3/4" copper pipe if you ream the pipe out on the ends after you cut it.
Bookmark this resource if you ever plan on using it.
I think they will look EVIL with 4 of them feeding my gatling gun......