You can do them yourself relatively easily if you've got some materials. Even if you dont do them yourself, i'll post this up for future reference..
1. Rotate the hub around so the stud can slide out the back of the hub (There is a cut out where it allows the stud to come all the way out)
2. Hammer the front of the stud, and eventually it will pop out the back of the hub.
3. Insert your new stud, grease up all surfaces
4. Place a large nut onto the front of the stud.
5. Tighten a wheel nut onto the stud. As you tighten it will push against the large nut and pull the stud into the hub. Tighten it all the way up until the stud is fully inserted (you will definitely feel when its all the way in).
Note: You will probably bugger up a wheel nut doing this, so make sure you've got a spare!
Have you tried Lincorp Nissan to get the studs? If not, I got some from UAS (seven hills). They may have R34 studs.