You probably won't be able to find either UE driveshafts or knuckles.
If you get the WideTrac and use the titanium turnbuckles that comes with it you need the old style knuckles/axles carriers like the
RPM T/E-Maxx 1.5 & 2.5 Axle Carriers:
You could also buy new turnbuckles like the
Lunsford Racing #2802 and then use the new style knuckles/Axle carriers like the RPM
Revo, T-Maxx 2.5R / 3.3 & E-Maxx 16.8V Axle Carriers: