Try to get them locally if you can. Fuses should be about 25 cents each that way. (might come 3-5 in a pack.
Online, you can get them for digikey.com, mouser.com, radioshack.com, etc. You'll have to pay shipping and maybe a minimum order. Radio Shack may waive the extra fees...I haven't bought anything from them in years.
Oh yeah...did you need fast blow, slow blow, or regular? (If it's for a power supply fast blow may trip due to inrush.)