i just replaced mine with the small plastic vacuum tubing from autozone. not sure what size...small...i think they only have one size there. i used heat shrink to ensure that the seal was air tight.
I've never replaced one of those lines, I just repair them when they snap. Use a peice of vacuum tube that will fit over it and connect the two broken peices.
You can get new bulk plastic hard line but I generally won't use it either. I do like the guys do, and use rubber line as a splice or even as a new replacement run. Either way works.
I use the hard plastic line, just heat them slightly with a hear gun to put in nice bends. Looks way cleaner than a ton of floppy slices in my opinion.