Is there way to find my USDA hardiness zone by latitude and elevation?

You could call the USDA in your area. I think the difference between 8a and 8b is negligible unless you are trying to raise some exotic not suited for a freeze. I'd say your local nurseries will only have stock appropriate for the area. There are micro-climates the southwest side of a hill with sun is going to be different than the northeastern side of a hill same elevation within a mile or two of each other. Some plants are more work than others but then again some are worth the extra effort.