A friend of mine showed me this, apparently she does audio work for erotic SFMs and other similar stuff, but among her works she also has done a few transformation related audios (example: a female to male werewolf one) which you can find here:
http://poisonousbeauty.tumblr.com/tagged/transformation
It is also worth noting she takes commissions
http://poisonousbeauty.tumblr.com/Contact