I don't have any, so I quickly made some. I cut the ends off some black Wilson socks, and I instantly had some slick looking arm warmers. They ended up working dandy, with the only problem being some fraying at the cut ends. This is only a problem though, if you want to reuse them.
I've decided to try and hunt down a pair of a real, honest-to-goodness, pair for the fall. I think they're the cat's meow. I'm sure a running store should have them, but I haven't ever seen them for sale.
Anyway: exactly 1 hour easy.