The WRR/X has a very different leverage ratio than most mx/offroad bikes.
If you do find one that will bolt on you will have to respring it with a 8-9 kg/mm spring (most mxers are 5-6kg/mm), revalve it to go with the much stiffer spring, shorten it and reduce the travel to what the stocker has.
My point is instead of doing all this work to some other shock, you could rebuild/revalve the stocker with a better seal head and a gold valve kit or get it done by gorace and have the same thing.
Theres plenty of aftermarket support for the stock shock, send it to gorace or buy the parts from racetech, they both have everything you could ever need to fix or mod the stock shock.
If the lack of schrader valve bugs you, you can tap the bladder cap for one quite easily.