You might find some good info in this recent thread although it’s more about right angled connectors: Angled connector for Elektron PSU
This was recommended in there:
Rockboard is German I think, generally easy to find in the UK and EU.
Edit: Just noticed you want male->male - that might be more of a challenge. I’d probably recommend just making some up yourself if you have a soldering iron as that might be a challenge to buy off the shelf.