That is tougher. The first place I would try is http://www.e-gunparts.com/
, which is Numrich Arms on the Internet. I know they have parts for H & R's cause I have bought some for my old .32 from them. Whether they have parts for the NEF, which I think are the same basic design but a little different from the old H & R, I don't know, you will have to check.
I buy their catalog every year (which you can order over the Internet for a few bucks). It is about 4" thick and has parts for just about every firearm known to man. It is worth it if you are a shooter.