A while ago i bought a generic cheap whiteboard off of amazon. The frame had some kind of T-Style profile in which the original pen tray was supposed to be mounted.
I made use of this profile to now also feature a bunch of keychain holders on the lower side of the board! :D
The sizing of the profile in my FreeCAD project is parametric. If you need any tweaks feel free to ask, maybe once i tidy up the project a bit i will also upload the fcd file.
Best printed laying on the side with some support for the overhanging parts
The author hasn't provided the model origin yet.