I´m in search for a source or good idea.

The Type A Mauser´s for example have those slingeyes , but there are no fitting hooks for the rifle sling to attach.
I know Winchester made them in days gone by.

Do you mean like the snap hooks used on Korean and Viet-Nam era rifles. It's a sheet metal hook that when slid over the loop snaps in place

No, not the snap type . Must be a simple hook made from an adequate strong wire and little tension so it will slip into the eye.

i just bought a set of orignals Winchesters on ebay for $40. you might check, I think the guy had a few pair form an old Winchester parts lot.

Two months ago I found a pair on ebay too,
but the owner was somewhat boneheaded and did´nt want to ship to Germany

Try Dixie Gun Works they used to stock exactly what you are looking for.

Exactly what I had in mind.