@Eamoex: don’t worry: a restock has been ordered - just talked with Adrian yesterday - a new batch is coming :-).
If you 3D print them, make sure to use a sturdy material, maybe ABS - as there is little horizontal space, the material cannot be too “wide” for everything to fit into a standard rack. You could also modify available 3U mount kits for other synths, in the end, the side panel only needs two holes through which you can fasten your SEQ v4+ with bolts, washers and nuts.
Best regards and enjoy!
Peter