There are definitely metal wheels available for N scale, many companies have made them. But metal trucks are another story. They are quite rare in N scale.
Since N scale was introduced in 1960, I can't think of any companies that have made diecast metal trucks, except maybe ONE company. Between 1960 and 1970 a British company called "Lone Star" made a lineup of N scale diecast trains, in their "Treble-O-Lectric" and "Treble-O-Trains" ranges. Treble-O-Lectric were electric powered, while the Treble-O-Trains were not powered, being dummies (push along). All bodies and frames (diesel, steam, freight and passenger) were made from diecast metal. The powered locomotives all had rubber band drive (like very early Athearn in HO). I have read that the wheels on the freight and passenger cars were plastic, and probably also for the dummy locomotives. I believe all equipment might have came with metal trucks, but I don't know. I looked at some pictures online, and the trucks look like they are metal.
I know other companies have made diecast metal locomotives, where the body shells and chassis are metal. But I believe all those models had plastic trucks. I don't know for sure.
There are also locomotives made from brass in N scale. I believe many of those locos have trucks made from brass. Also in N scale some passenger, freight and cabooses have come with brass trucks.
Other then those examples, I can't think of anything in N scale that ever had metal trucks. Certainly not the regular N scale you find in a hobby shop.
If you want to combine metal trucks with metal wheels, you need to be careful you don't create electrical problems. If the axles and wheels are all metal, they can possibly short out when combined with metal trucks. You would need to make sure, everything is properly insulated from each rail.
Hope that helps.
Howard
