How can I find a PS that specializes in parry-Romberg? Interested fat grafting on face for loss of volume on my cheek. (photo)

This is a good question. I have done several of these cases with Fat Transfer. It is a very good treatment for this problem.  The fat lasts and stays and ages with you. It is the preferred way to treat this condition in my practice.   I have long term follow up as well. I have been doing Fat Transfer since 1993 with great results. The Fat is transferred from another area and re- injected into the problem area. It is harvested via gentle liposuction, then centrifueged to separate the fat out.  Once this is done, it is injected into layers into the problem area.  In your case it would be your cheek area.  The goal is to achieve symmetry with your face.  Other procedures such  as a cheek implant would not be suitable due to the nature of Rombergs progresssive facial lost.  The results for this are wonderful.  

 The treatment to your condition is complex and should not be addressed with a simple single procedure approach.
Facial skeleton all imbalance should probably be addressed first.
Attempting to create for symmetry with you so fat transfer may not lead to a satisfactory results.
I say this for two reasons.
First, fat transfer cannot create the amount of volume you will need to create symmetry or not nearly as well as other options.
Secondly, adding fat where there should be bone structure for volume and support support may not look the same and will create a new sense of imbalance.
Your best bet is to seek out an experienced board-certified plastic surgeon who has craniofacial experience.
This may very likely require going to an academic center in finding someone who it's fellowship trained in craniofacial surgery.
And accurate work up should be done first with proper assessment using MRI to determine true deficits of bone and fat.
An accurate and precise treatment plan can be put together which would most likely include fat transfer but may include other options as well 
If you want to see what soft tissue volume can achieve for you then I suggest using hyaluronic acid based temporary filler's such as Restylane or Juvaderm.
In doing so you should understand that fillers can create an unlimited amount of volume one fat transfer is limited in how much volume can be achieved with a single procedure.
Fat transfer can only add a certain amount of volume per procedure.
Over grafting with fat simply leads to a higher degree of fat resorption. To gain the long-term volume needed you may need to have more than one fat transfer procedure.
hyaluronic acid-based fillers can be reversed by injecting an enzyme.
This is important should you at tempt treatment with fillers then want a proper assessment for a permanent surgical solution.
I did my training and plastic surgery at the University of California Irvine.
I know many of the top-tier plastic surgeons in the area.
Feel free to send me a private message if I can be of assistance giving names of plastic surgeons that are on top of their game.
I would avoid the temptation of looking for a simplistic treatment to what is a complex problem.
Best,
Mats Hagstrom M.D.