Oh, yea, one wheel drive stinks. The town & Country's had open differentials. One of my temptations when I build a trike is to go to a solid axle. It has it's problems too. The bike wants to go straight when you want to turn unless you lean it so that the inside wheel spins. When I looked up trikes for this response it seems that most have one wheel drive including Schwinn. It is Pacific now marketing as Schwinn so it's not the same as the old Chicago built Town & Country.
I did find this video from Utah Trikes. But this is a bunch of work and parts to get a differential.
The Samagag website looks like they gave this product some engineering. It has a forged body and uses bevel gears. They seem to provide axles and hubs as well. But how do you buy this stuff, how much does it cost and can you talk to anyone about what your specific needs are?
samagaga.com/WhatsInsideDifferential