Here's another really good nursery in Mississippi that sells roses grafted onto Fortuniana. It doesn't carry the Knock Out series, I don't think, but it has a good variety of other roses. I've bought roses from this nursery and they're spectacular. Fortuniana is not a hardy rootstock, so it's not for everybody, but it works beautifully in California and in the southern states. Most of my Fortuniana-based roses are easily twice as tall and wide as other roses in the same beds.
http://www.kandmroses.com/