Sue, HMF does have a clematis section, but I find their choices are really limited. About half of the ones I currently carry are not listed there at all... and some of the ones that are listed have incorrect info. That's part of what inspired me to go ahead and create a database here. Currently, you really need multiple sources when looking for clem info (though I hope to change that by compiling it all here!). I currently look at Clematis on the Web, HMF and one or two other sources when selecting clems.
HMF is unrivaled, though, with their roses database!