Nic,
I had a bunch of problems with blinkers, stop lights etc... I found that corrosion along the entire system ie.. the switch plug points, bulb sockets, factory but-connector, etc... all had corrosion that was over causing excessive resistance and therefore overheating the system. My switch would get so hot that the main power wires would de-solder themselves from the switch. After re-sodering them twice I began to investigate all the wiring and that was when I noticed the corrosion. You can't see it untill you pull apart the connectors, but I garuntee it is there. After I went thru and cleaned all connection points and once again sodered ( i know i am spelling that wrong) the power wires I have not had any problems. In fact the light intensity was substantially higher. Funny how that works!!! I don't think you are going to be able to get the part new that you are looking for. No Nissan dealer ( at least around here) has any type of electrical parts for the old Z's.
Rufus
EDIT= I stand corrected VB has them..see this thread
http://www.hybridz.org/phpBB2/viewtopic.php?t=28646&highlight=