Harris sells these.

http://sheldonbrown.com/harris/accessories.html#bottles (scroll down a bit)

I use them and the work very well. They are a heay duty plastic so the wont scratch your frame or rust. The mounting bolts are stainless as well. You can order them through any shop that deals with QBP (Quality Bike PArts) and they will be cheaper. I bought 2 sets for $20 through my LBS.