Funny that you are inquiring about this, I am also on the hunt for some inserts. I tried monroe today for the N10 pulsar struts to no avail. they claim that they have no stock, and no longer manufacture them.
I am still not sure if anything will fit mine, as I have the australian assembled 120y PBR struts (no nissan markings on the strut) that appear to be a smaller bore than the Nissan ones. They measure in at 38.5mm ID.
Either way I am going to chase a few other places tomorrow to see what I can get my hands on. I'll let you know what I dig up.