https://www.tgauge.com/product/193/0/19-metre-motorised-chassis Have you checked out this place? It's growing quickly and the resources are getting better all the time.
Eishindo produces the only power chassis, offered in various lengths. Eishindo is actually the only producer of commercial T Gauge. The motor and gearing are all identical, and only the rear truck is geared. For different lengths the forward truck is just extended further away from the motor. As you can see, all wheels provide power. Locomotive wheels are magnetic to increase contact with the steel rails. I find a single power chassis is capable of reliably pulling approximately 4 cars, so powered freight cars will absolutely be required in this scale if you want long trains. Here's a future F7 unit, once the ACe is complete.
Got a question! Is there one of these motors with a double shaft like Rokuhan has as a part buy. In Z scale we started using the Rokuhan double to have front and rear power. It seems this frame one end mirrored for the power could make it double powered. today it seems possible to do this!