You can no longer get the regulators, Lionel has discontinued offering them. They declared all the TMCC and early modular Legacy electronics as obsolete and removed them from the website. That was an extremely low class move!
The way to fix the smoke is to rewire it for unregulated operation and change the resistor to a value to a 2 watt wirewound resistor from 20 to 27 ohms.
For your reference, here's a Motherboard Connections R1.31.pdf, your engine motherboard is a 691-PCB1-10D, it's on page three.
