It took forever to find this little brush, but Liz at Wet Paint came through for me. And now they carry them! Thanks!
"Koi water brush". I don't really see a model but the numbers "xqr" and the numbers 38552 and 4ml large are on the pack. These come in three sizes but I have only played with the medium.
I love it and Perfect for what they do and the size, but my critique is they are a lot harder to squeeze and don't have the water control of the larger sizes. Easy trade off for portability, but planned sketch day would benefit from the larger brushes. The water cartridge travels really well, but be warned it doesn't hold a ton.
Now with my Altoid kit and a rubber band holding a paper towel I have had a blast being able to paint with (almost) as much portability as a pencil (almost, but certainly more colorful)