You can order the thrust bearing and seal kits from several sources like ITS or FadalCNC for around $90 per axis.
The ones I just got from ITS were NSK bearings and had the preload shim with the kit, and all the required seals.
I just did all mine this week and it's pretty simple, especially for me because I removed all my screws to be reworked so my bearing carriers were already off.
Just make sure the thrust bearings are face to face, in other words, the thick side of the inner races will face each other. The shim goes between the faces.
Make sure you get the correct kits. There is one from metric screws and then inch screws. With yours being a 1996 I would imagine they are metric.
Richard