If you have insurance or an Employee Assistance Program where you work those are great resources for referrals.
Otherwise...you can literally do an online search for therapists in your area, often by specific issues (sex, marital counseling, etc)...you can find them listed out with their specialty areas.
I would suggest calling a few of them and sort of doing a brief over the phone interview. Give them a brief overview of the issue you are experiencing (finding other women sexually appealing, but not your W even though you love her)....let them know you want to work past this for your M, ask if they think it would be beneficial if she participates at all....and then ask what their approach would be and if they feel they could help you.
If someone won't talk to you briefly over the phone, don't go with them. I've found that a therapist who really cares about what they do and really wants to help, won't mind taking a few minutes out of their day to answer a few reasonable questions from you....prior to charging you for their time. I used this method to find our MC, she was the only one who returned my call.....and we've really been quite happy with her.
