Fully parametric in Fusion 360. You can have as many spaces as you like and adjust all of the dimensions to suit your collection. 

There's an experimental “stacking” parameter which will create a little cutout in the feet to (in theory) let you stack the holders vertically. Don't be put off by the Combine operation giving a warning!

There's also a pre-made STL for a 5 pen holder that's 150mm long and 25mm high.