Microscale does decals in N. Many of them are the same as HO, just replace the '87' attue stat of the product number with a '60'. There are others.
Search around for BLMA parts on ebay or online stores, there's still stock in places.
Gold Medal Models see
here. Hope someone keeps producing that line but we'll see.
Miniatures by Eric has a bunch of detail parts
For lighting stuff there is Ngineering and afaik Richmond Controls is still in business.
Detail Associates had a few N scale parts but at this point what you find may be old stock.
Sunrise had great stuff but is gone so anything you can find is lucky.
Be more specific about what kind prototypes you'd like to detail and people may have more specific suggestions.
.