This summer has been hard on any rubber stuff in my garage. My spare tubes have all dry-rotted. Worse than that, the hose on my old Nashbar bike pump developed a ton of cracks and started leaking.
I found a cheap fix and now I'm back in business! 3/16" rubber fuel line from my local auto parts store fits perfectly.
You can also buy replacement heads and hoses online, but the fuel line seems to be quite a bit better quality -- hopefully car fuel lines don't rot to pieces every ten years -- and you can make sure it will fit at the store rather than order and hope.