Try this link Henk
http://www.racing-cars.com/pp/Old_Ca..._SX/U3298.html
You can get the spring washers with the new diff screw again from Schumacher. This has the diff screw for the 23mm Bosscat pro diff but has the spring washers.
http://www.racing-cars.com/search.asp
As for the thrust race the plastic cage has a tendency to disintegrate, they did eventually replace it with a metal one. I've heard people remove the cage and add an extra ball instead.
The part number for the thrust race is U1954V they do turn up on eBay and places. If you look for the part numbers you should be able to find most of it cheeper than on Schumacher's website.