heyMatt; Few plant-oriented web sites have info on the heat zone ratings for various plants. The best one I have found is Monrovia Nursery's web site plant catalog. First look up the plant of interest and then click on the 'Growth' section. If forum members know of other helpful sources they should inform us. Disclaimer--I am in no way associated with Monrovia Nursery. Regards, heyMikey!!
http://www.monrovia.com