My own test leads have increased to large numbers.
Binding post banana cables of all types, cables for multimeter, oscilloscope probes, battery charging special cables, BNC type cables, and more.
Your search for a test lead holder (organizer) will lead you to American market, which this is not an option for Europe due aggressive shipping costs.
I did several hours of searching for a close alternative and I found it !! at the section of cloths storage solutions.
For just 1.5 Euro you can get one or more from these hanger for ties, next step this is to remove hanger hook point, and to mount this plastic over a flat surface.
(You can use screws or cable ties)
Depending the length of area that you have available, you may select quantity of them that you can use.
Speaking of color selection, all boys can get blue or green.
Keywords in your own eBay search: Closet Storage Rack Tie Belt Organizer hanger