We just had a really good freestyle clinic here in GA with Cynthia Collins of Luna Tunes. Most folks came in with music in mind (brought in their ipods, etc.), but they ended up using other music from Cynthia's extensive library because it suited their horse better. One person had a freestyle that had been designed by someone else, but it was pretty obvious it wasn't going to work, so she scrapped it in favor of one designed by Cynthia. It was really educational and fun to see the horses "picking" out their music - very obvious how they liked some pieces and didn't like others.
She provides tempo matching, music selection, choreography, computerized editing, etc. - pretty much will handle as much or as little of the process as you need. She has a lot of successful clients (including Hilda Gurney, Debbie Hill, Whit Watkins, Heather Mason, etc.), and her prices seem quite reasonable - looks like they are based on the level of freestyle (i.e., $700 for Training / First Level, up to $1200 for GP). Her web site is http://www.lunatunesfreestyles.com/ .
How about Adrianne or Stephanie? Stephanie Alvord
Stephanie Alvord is a USDF Gold, Silver, & Bronze medalist and she has earned her Gold, Silver and Bronze Freestyle Bars. She has also earned the German FN Bronze and Silver Reitabzeichen (Riders Badge) while training and competing in Germany from 1994-98. Currently, Stephanie rides her Oldenburg, Dreamboy, and together they have had competitive success at Intermediare and Grand Prix. She is also competing with Graf Alpha at Intermediare. Stephanie coached the United States Pony Club Quadrille Team, winners of the Quadrille Freestyle and the USPC Robert Dover Freestyle Pins in 2008. Stephanie owns and manages Clover Hill Farm, in Waterford, Va