Hofvijver Grijs is a nice middle-of-the-road gray (unless you prefer that it be grey) ink from PW Akkerman.
If you’ve been searching for a US source for Akkerman inks and their iconic bottles, check out Vanness Pen Shop. I’ve only ordered from here once, but had a good experience.
It is much less expensive to purchase directly from Akkerman in the Netherlands, as long as you are willing to purchase 4-5 bottles at a time (including very high shipping costs). Not that I am opposed to purchasing from a US business, however Vanness charges more than double the cost per bottle.