A couple of thoughts,
The gears you seek are going on 40 yrs. old.
To find any in good condition (not cracked) is low probability, these could come from a donor lokie from perhaps eBay or from a fellow modeler.
Still don’t know what condition you will get other than 40 yr. old gears.
That’s going to be a gamble you may, or may not, be willing to take.
You can search N scale parts on the bay.
Another option that may be worth considering is from NWSL.
You will need some calipers and have to know center bore diameter, outside diameter, and tooth count.
Then call and ask them if they have anything compatible.
Were it me, that would be my first choice.
I have some old trucks, maybe the gear you need, dunno, have a look.

