I think this[1] is the one "Wheels" uses but it's pricey and sold by a UK company though it appears they ship to the US for a flat rate £10. There's also this one[2] which is a similar design and just as pricey.

[1] http://i-walk.co.uk/product/urban-2-foldable-electric-scoote...

[2] https://onemileusa.com/