Are you referring to Nickel plated or actual Nickel Silver rail? They are different.
Not sure if there are any pieces out there, but LGB (before the end) introduced a new line of Nickel plated brass rail. Probably going to be hard to find since this new product line came out near the end of LGB.
Nickel Silver (NS) is typically solid rail and not plated. We use NS on both the HO, and G scale layouts. I can't comment if it's is better or worse then Stainless Steel (SS) since I've never used SS rail, but the two would probably work together fine. I do use SS rail joiners on NS rail and haven't noticed any problems with electrical conductivity. I did notice electrical problems when I used Brass rail joiners. After switching to SS joiners, no more problems.
Not sure if code 332 NS is available, but we use Llagas Creek code 250 NS rail. Aristo rail is code 332. LGB Nickel plated rail is also code 332, but finding it is likely not worth the effort.
I use the Llagas Creek code 250 nickel silver rail and it works fine. If you go with flex track you will need a rail bender as it is very stiff. I do not use track power, but nickel silver has better electrical transmission properties than brass in that it doesn't oxidize as much.