Rare to come across nowadays.
I've compiled a set of PDF's and docs on the R34 that people have found useful:
http://www.mediafire.com/download/kfp0g2vulagm88v/R34.rar
Contains:
A book of skyline stuff (lol)
R34 10000KM Maintenance
R34 ECU Pin outs
R34 GTR MFD Manual
R34 Interior fuse box english translation
R34 NZDM brochure
R34 Service manual
R34 Stereo pin outs
Nissan Paint code index
Nothing near a users manual but you'll definitely pick up some stuff from the lot. General operations of the vehicle, just post a thread here
Skylines Australia - The Imported Manual-less car owner's manual*
*Certain excerpts may or may not be correct. Some advices and instructions may lead to more headache and frustration.