I couldn't find a holder that worked quite for what I wanted, so I made a simple cartridge and vape pen holder. I have two vape pens of different sizes - one has a diameter of 17mm and the other is 11mm. I've oversized each socket by a mm to allow for wiggle room.
Please feel free to edit the design at the link below. Criticism always welcome.
This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/7XjsZxYzOSV