Pokemon Adventures Black 2 and White 2 Volume 3 is apparently releasing in the US on April 13, 2021.
That might just be a placeholder date, but at least we have the Amazon listing. I can't seem to put a Amazon link here, since it's deemed "spam-like" by the board software. But if you search for "Pokémon Adventures: Black 2 & White 2, Vol. 3 (3) " you'll find it.
There doesn't seem to be a listing for volume 4, which is strange, but understandable if the release really is that far out.