Cannot find Vendor for Material

I am to create a Purchase Requisition for a custom defined Material in the Global Bike Inc. example database.

I would like to filll in the Required Vendor field, and search there for the Vendor giving the Material. SAP does not find the Vendor.

I give both the Purchasing Organization and the Purchasing Group in the Purchase Requisition.

In the Purchasing view of the Material, I can give only the Purchasing Group, but the Vendors by Material search dialog box insists only on Purchasing Organization and does not find my Vendor for this Material.

How can I assign my Material to my Vendor?

UPDATE: I have found that I need to create a Source List for a Material where I assign my Vendor to the Material. I did it, but still, I cannot find my Vendor through the Vendor for this Material search window. What shall I do to make it work?