When I was stationed in Kirch-Goens, Federal Republic of Germany in the early 1970' s I purchased a nice side by side Eibar in .410 at the local military " Rod and Gun" Club. It was made in Spain, reasonably well finished, and did a decent job on the Trap Range (when I stayed at the closest stations). Unfortunately I do not have any information about your particular shotgun.

You are right in your speculation that it was made in Spain. If I am not mistaken Eibars have been imported, at different times, under different import licenses, and different named companies. (Which does not make it easier to track down the particulars.) I would continue to explore different avenues using different " search engines" on the web....until I tracked down the info.

Good luck with your search!

P.S. Good advice...keep it until you are sure what you have!