I miss Phoenix desperately but did not grow Clemmies when I lived there. This article might help.

You should ask and look at independent nurseries rather than big box stores. Big boxes often stock plants that won't grow locally. Here they stock stuff I grew in Phoenix and in Phoenix they stock stuff for here...

If I remember correct, Baker, Berridge and Whitfill Nurseries were very knowledgeable but it has been a long time since I lived in The Valley.

Here is a link that might be useful: Clematis in hot climates