It’s unclear if you’re imagining that power is provided along the line or if these will need to be self-powered.
If you’re looking in New England specifically then the rolling stock of MTA Metro North or CT Rail might be of interest. Assuming the protagonists will have access to a power source. I think Hartford Line CT Rail uses both third rail and overhead power, so that might make for a point of discussion about them seeking out these specific units for their more flexible powering options and voltages.