First go to an internet parts seller like eBay, Craig’s List... I got lucky and found a pair off a brand new 08 yz450f that a dealer was parting out! They came with the triple clamps (not needed), and axle which came in handy later. Now for those who don't know the forks are the same diameter and will fit in the stock WRF clamps, there are however many differences. The hub, axle, spacers, and brake caliper are all different. The hub and spacers are because the YZFs don't have the speedometer, and the YZF caliper uses a smaller mounting bracket, probably due to weight. You can however use the stock WRF setup and here is how.
In this image of the stock WRF, you will notice the space in-between the axle clamp and the wheel spacer. The clamp should not come into contact with the spacer; the larger diameter part of the axle is what should tighten down to the spacer. The next thing you will need to do is make a spacer for the axle. An YZF axle is too short to fit on a WRF. The WRF axle is longer than the YZF axle, but it is a little too long. The tapered part right before the threads will bottom out on the tapered part of the left axle clamp.
This will put all of the pressure from the nut torque on these two points, so the wheel will still be loose. To solve this you will need to make an axle spacer that will go on the axle and extend the larger diameter part a little to move the entire axle over to the right.
I used the new axle that came with the forks, but you can use anything that will fit over the axle and into the axle clamp. After trying a few different sizes 5mm seems to work the best. The YZF axle clamp is stepped over and wants to have the clamp come into contact with the spacer. To fix this you will have to file the lip off of the YZF axle clamp. I just filed until the lip was gone, and I could see light between the clamp and the spacer.
The YZF clamps don't have the lock for the speedo spacer, so you will have to position it where you want it before you torque down the nut. Once it is torqued down it will not move, unless you don't have the spacer wide enough and the pressure is on the tapered part of the axle and axle clamp. The axle will stick out of the right side, if you don't like it you can cut it off but it will no longer have the alan head cut to hold the axle when you tighten the nut.
The fork guards are also not compatible, so you have to get a little creative for the speedo cable.
Nothing says creative like zip ties... To get the brakes to work you can either order a 06-09 YZF brake caliper, or modify the original. To use the stock WRF caliper first mount it on the bike using the bottom bolt then center it by looking through the other side of the wheel and lining up the brake pads with the wear marks on the rotor.
Then mark the location of the top mounting hole on the caliper hanger with a pick, pen, or just something to mark the location of the top hole on the hanger. Remove the caliper from the bike, and then remove the hanger from the caliper. Drill a hole on your marked hanger and tap it to 8mm x 1.25 pitch. Then file the ribs to make the mounting surface flat, and make a spacer to center disk to the hanger. I can't give a specific width because you will probably remove a different amount from your hanger than me. This will require a few attempts to get it right, just have patience and make sure the disk is centered.
The brake line had to be moved up a bit because it was a little too close to the spokes. The white dot used to be level with the clamp.
Now make sure everything is tightened down, and go ride!