Not certain of what is out there now, but Atlas O has announced their 21" Horizon cars (will run on 0-54 curves), one roadname of which is NJ Transit. Looks like seven car numbers, including a cab-control car will be produced. If you know a dealer that carries Atlas O, pre-orders are due in August, with deliveries tentatively scheduled for first quarter 2020.
There have been previous production runs of these cars, but their availability is something for others to testify to, as I haven't looked around for them since getting mine many years ago. In the same vein, MTH made NJT versions of their Bombardier double-deckers, but those have little in common with NJT's multilevels, if that is something that concerns you. They might be easier to find for this reason, though.
---PCJ