Miloslav Zacharda was the stand-out expert on this topic, but has now retired. You could always try getting in touch and seeing if he has recommendations. Other than him, I'd look to other "nearby" acarologists who are experienced enough to be able to use Miloslav's excellent work. Alternatively, you could look broader than Rhagidiidae (I don't think anyone is focusing on them now) and see who's active in Eupodoidea. Alex Khaustov springs to mind immediately although he may have moved onto other topics now.