Skirt guards are hard to find in America and can be very expensive. Cable ties and scraps of tulle or other mesh material will keep your skirt safe without going to the Netherlands or haggling with a collectibles dealer. You can read about the inspiration for this project at www.evilmadscientist.com
You'll need a bike with fenders, a handful of cable ties, and a couple of pieces of tulle or mesh slightly larger than your fender. A cruiser or touring bike will work best, but you could adapt this to a bike with a cargo rack or a seat post mounted fender with a couple of holes drilled in it. Tulle is cheap at any fabric/craft store (mine was on sale after halloween) or can be scavenged from old formal dresses. It is reasonably strong and doesn't hold dirt very well. You can spray it clean pretty easily, too.