GESI is a popular one because it can handle forced induction. Check out the GESI site, you will see options for just the cells so you can size what you want as well as transitions. Once you find what you want, shouldn't be hard finding a vendor.
Nope but GESI has totally stepped up their product line. I'd say they've closed the gap on HJS market shares.
Keep in mind Performance Ind. operates on a three tier system. https://www.metalsubstrate.com/