Find binding in UI Designer between sales quote and sales order

Dear Experts,

I have created an EC to link Sales Order to Sales Quote Manually (We don't want to use standard new SO creation we want a custom view with custom listmodification form) , But I am not able to find association in UI designer to bind my list hence I checked standard QuoteUI designer.and it is binded to standard CustomerOrderReference which I am not able to find in BO Model. Below is standard binding. Can you please explain this? Shall I write an incident to SAP to make this available?

Kindly suggest! Thanks a lot.