We are in Ohio.
I'm NOT asking for individual recommendations - I would just like some general "what to look for" and "what questions should we ask" advice.
Based on this response it appears you just want to know what qualities or teaching method to look for as opposed to a specific instructor or how to find one. This may be a little unconventional with the majority but it seemed to work with my son and his success. He tried 3 different instructors and the last (current) one was the best fit for him (12 plus years). Note: my son is a position player thus this may be skewed towards that and not a pitcher, but same principles.
I truly believe just by being a great athlete with baseball talent and ability can only take you so far. You have to be a student of the game, to understand and learn the game better than others. This in combination with talent and physical ability will give you a better chance of standing out. His instructor used to spend a minimum 10 minutes talking to my son, seeing where his thoughts were, asking him situational baseball questions and scenarios, strategies, etc (this started at 9 years old).
An instructor who works with the kid to tweak his mechanics based on what is comfortable for the kid's body and strength. As the kid matures and grows his strike zone changes, he gets stronger and bigger thus mechanics change.
An instructor who listens to the kid. When my son suggested things, if it made sense he would let him try it. At the end of the trial period they would discuss the results. A few times on his own son realized his suggestion didn't produce desirable results. Few time a week later son forgot his suggestion from prior week and went back to old way. Every now and then something works, and if it somehow got his bat on a better swing path, or arm slot for pitching then that was emphasized. What this ultimately did years later was create a unique baseball bond between student and instructor where an open line of communication was easier. No longer was it instructor "telling" student what must be done, it was discussion and end result. Son felt he had more control over his learning and abilities since a joint decision.
Sorry this is a little long and boring. PM me if you want more details.