My advice may be a little different from others. If you are looking for an IC as opposed to an MC, then looking for someone who specializes in infidelity might not be who you need.
Think of it this way. If your car breaks down, you need a mechanic to fix it. If you need to learn to drive however, then you need to go to driving school. I mechanic can't teach you to drive and a driving school can't repair your car, even though they may both specialize in automotive services. Therapy can be similar.
Infidelity isn't a mental disease, rather, it is a failure of character. You can't "fix" infidelity, that would be like asking the mechanic to fix your driving. In order to become a better driver, you need to learn a number of skills, among them, confidence, patience, how to monitor the road for danger, how to react in a skid, and so on. In order to be a better partner, you need to learn self-respect, grace, integrity, honesty, how to manage conflicts, how to face failure and temptation, etc.
My point being, an IC can't exactly "treat you" for infidelity because it doesn't work that way.
What an IC CAN help you with is working through your "why's" and how your character flaws came about, and most importantly, how to go about making changes in your life to be someone better, someone you can be proud of, someone who would never debase themselves in such a way.
For me, I found that IC's who with AMDR often were helpful to me in terms of going back to childhood and sussing out some important parts of my life that left me in the broken shape I was in. Once I learned why I felt/acted the way I did, I was able to take steps to counter those broken ideas and messages, and replace them with healthier ones. As backwards as it may sound, this is about fixing YOU, not your marriage. However, fixing you is a prerequisite to fixing your marraige! Going back to the car example, you may be ready to learn to drive, but if the car isn't running, you aren't going to get very far, so you have to fix the car first. In the same way, the WS has to fix themselves first, THEN they will have the skills they need to R (or D).
I would search for IC's who understand trauma and childhood issues. (If that's your story). If sex addiction is an issue, you may want to head in that direction. Either way, it takes time and effort to find a good IC. I went through about 1/2 dozen before I found on that I clicked with, but when I did, it made all the difference in the world.
Best of luck to you.