Dynamo here on ASC is making and selling flute valves:
http://www.airsoftcanada.com/showthr...=147346&page=5
Towards the bottom of the thread, back in September, he said he's been too busy with work to make these, though. You can keep an eye on the thread if you're patient.
My friend has one of his valves in his KWA MP9 (was originally purchased for an M93r too), and it works great.