Roadworks Synth Holders

Hello,

I just bought a Roadworx 4120b and I want to put more synth holders on it, but for my surprise, Thomann just told me that they don't sell any accessories for Roadworx. They also said to me that Jaspers holders don't fit on it.
Where can I find some synth holders that fit in this? I thought that holders are stuff that is adjustable or at least they are universal. I was looking for something like Holders 30B

All the help is very appreciated