In the UK, ExpressPro sell their own Ex-Pro branded version through Amazon. There seems to be a good range of plates available for sale either with a base unit or separately. ExpressPro seem to be one of the best of the Chinese goods resellers. They appear to be pretty careful about what they choose to put their name on and offer a good service.
That's cool, but fyi, those plates (and the charger they go on) do not look like they are the same as the ones the Neewer charger uses. They might not be compatible, (although from the photos, even though the plates are different, they do look like they might be physically compatible) and the dual charger is certainly a different unit without the much desired LCD read out.
I know of at least two completely different plate systems available.
Lenmar was the first to do this, going back to at least the late 1990s,. and they still support that system. Haven't seen any on Amazon in the US, but a google will lead you to them. Plates are usually around $5.00. Adorama sells them for $3.00!!
The more recent one is Watson. They make all the plates easily available.
I am not at all sure why the plates found on so many of these Chinese parts like Neewer and Wasabi are hard to find.