dont hold me to this but it but.
I'd swear someone told me you can get these screens, or I'd seen em some where.
Nissan head office, have made the choice to only sell complete injector I recon, could be wrong.
It kinda makes sense from their point of view I guess.

So forgetting that, what the heck happened to the stainless filter, inside injector causing you trouble?.
These thing don't disappear by them selves!!. very strange.