I'm a stupid schmuck :D
IT IS STILL IN STOCK. That part about hard to navigate.. Just did a search and
it is categorized under "Brush Pens » Pentel Aquash Watercolor Brushes &
Crayons". Oh well I'm glad.
I'm sorry to see that you have stopped carrying this (the brush pen itself), or
if it has been discontinued. Was looking to try it - reading it is waterproof
perked my interest, but I can see why people didn't jump on it, especially with
the possible confusion towards the Pentel standard which also had a grey refill
and that these parts were kind of hard to navigate on Jetpens if I remember
correctly, when the brush pen was in stock.