You can get nismo ball joint's from SRB for around £100 for both side's.
but you have to get the old one's out, Not hard but you will need to press the new one's in, You could also go to the local factor's and ask about them also I did notice when I did mine a while ago that the nissan primera
one's look the same.
Oh and they where only £14 at my local factors. I had to buy one because I lost the boot of my nismo one I still have it the garage if you want it mate, You would just have to reuse your old boot

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rob