Just checked out the website again myself. It looks like the standard red floats are for 9-11 gallon casks and are 22.5 inches long. The "self cut" clear floats can be cut to about 15" according to the product description. That's definitely not roomy enough for a 9" diameter corny keg, so it looks like the DIY float is the way to go.
EDIT: I am a dummy. I thought those measurements were the float heads themselves, not the float + tube. The floats themselves are reasonably sized-- here's a writeup at homebrewfinds.com on using them in the fermenter/serving keg:
http://www.homebrewfinds.com/search?q=widge
Just ordered some 1/4" silicone hose. Will update with results when I get it working (or not).