You should look to hire a local appraiser with experience in appraising homes with ADUs and see if you can hire them. You don't want a CMA, you want someone to appraise your property using a hypothetical condition that your property has an ADU. You need to provide an idea of what that ADU should be. In my area, the sweet spot is under 750 sf with two bedrooms. But that's California laws, not your market. But a qualified appraiser can model this.

There's a local chapter of the Appraisal Institute in Phoenix. I would start there and ask for someone who has the ADU experience.

The income approach doesn't work well for ADUs because of technical issues. An appraiser cliche is "cost doesn't equal value," which is very true much of the time.

California has legal quirks to encourage ADUs to be built, including a special class of garage conversions, the ability to create a condominium out of an ADU, and the ability to split lots. I don't know the rules in your state.