Google knows. Or http://www.bikeforums.net/showthread.php?t=311322 has oodles of info on making your own. I did. Well, my mother did. She quilts and had some additional spare time... Have a light weight one made from an old flannel shirt, and a heavier duty one made from corduroy with a flannel liner for the fall weather. Know anyone who sews? Sew yourself? Might be worth it, a completely custom-to-you cap is a pretty snazzy thing to have.

Particularly, piratelove's posts, like this one: http://www.bikeforums.net/showpost.p...5&postcount=56