Have you checked with IKEA? They make that device, using Sonos internal electronics. 

Looking at the pictures on IKEA.com, it really isn’t clear what kind of plug is at the end of the cable, or in the speaker itself. If it’s a standard PC design, a figure 8 design, often called IEC-320-C7, or just C7, then you could get pretty much anything you wanted of the appropriate length, based on what I see on Amazon. 

But if it’s not a C7 connector, please post a picture, so we can give you more feedback. 

According to IKEA, this black SYMFONISK power cable will work with the picture frame even though it has a right angle plug rather than a straight plug:

https://www.ikea.com/us/en/p/symfonisk-power-supply-cord-textile-black-90492324/

So, it is a standard C7 connector. 

Worst case, wrap black tape around the parts of the cord that needs to be black for aesthetic reasons!