The drive unit is 6100.700. We did sell out last week and are waiting for more to arrive, you can order them on Tunze.com. Most dealers don't stock many spare parts but Premium Aquatics and Salty Critter have both stocked these periodically and may have them on hand.
If you have the 7410.602 transformer, no upgrade is possible, that is the most that pump can do, if you have the 7210.202 you could upgrade. I would question the wisdom of doing it though as I would not personally invest $60 per pump ($90+ with drive units) for something that is likely on numbered days. These pumps are at least 5 and as much as 10 years old and near the end of the life you can expect, the major parts of driver and motor are no longer available and a smarter investment would be newer pumps.