Because I didn't like any design out there, I decided to design one myself.
This modular design allows you to print as much holders as you need.
The holders could be mounted on top or on the wall - just mount them directy in your own desired distance or use the plates to have a defined distance between them.
The 90° bracket is just another option you may like. ;)
In this case, you have to screw the holders together with a M5 socket screw...
PLA or what you like