Wow, you aren't kidding you can't find them. Printed on unobtanium paper.
I've done this before for myself - NOT FOR RESALE - but have bought the HO sets, scanned them in a high-quality scanner, photoshopped out the blue background tones into white/clear and reprinted them smaller on clear laser decal paper to make some N decals. Needless to say, this won't work for white lettering at all, but looking at the 87-962 set, it might work as a last-ditch solution for what you need like that dark 'streamliner' script or some of that. There are some oddball decals they never made N sets for but did make HO. I've also done that with some truly awful ancient surviving HO Champ decals by applying them to white styrene and scanning that and reprinting it that way, again, white won't work but other colors can come out pretty well that way with a little tweaking. With the Photoshop edge detection you can even clean up the yellowed parts of the decal film and clear that out.
Even if you do find a set, make sure you put on a coating of liquid decal film to save them from shattering. I just got a set of Seatrain decals that I thought were relatively 'fresh' and they literally went to shards as soon as they were moistened. But I've saved sets that are now close to 40 years old with that liquid film.
