They are getting hard to find. I bought one recently from the app Mercari.

By the way, the item number 1VY59AA is also the HP Zbook X2 Pen. I don't know if there's a difference between the two. Doesn't seem like it, so you might get more options by also searching for that.

I found some oddly cheap ones here. They also have the 1VY60AA listed if you scroll down. It's a risk because a lot of these websites list this part for cheap and it's actually just the extra nibs without the stylus.

This site also has some. Not sure about the shipping rates. The pen was around $100 prior to being discontinued, so $95 isn't an absurd price.

Besides that, you might have to just keep an eye out on Marketplace and selling apps.

I can say that I love it. I came from a Tab S3 pen and it's substantially better.