Here are some props for a Walkera Runner 250. They are right at 6", just a little shy though. But they should work. You could always just get some 6" props and get the locking nuts for the CW and CCW threads. Most hobby shops will sell them. If not, you can get them online.
Here is what I came up with in a search on google. without having the motors here to measure the threads per millimeter this is about as close as I can get.