Vendor List with Backend Contracts not available as Sourcing in ECS scenari

Dear Friends,

We are working in ECS scenario where in we would like to refer to backend contracts as source of supply in Shopping Cart. So we tried to create vendor list with backend contract.

But such vendor list are not appearing as source of supply while creating shopping cart in Extended Classic scenario.

Does it means that vendor list with backend contracts are applicable for Classic scenario?

is it the standard functionality?

Has anyone come across this business requirement?

Please help

Sandeep Parab