I have a Garbi 16GA SxS Mod. 100. Best thing to do on these Spanish guns is to contact the importer you listed. They are typically one of only a few importers for the manufacturer, and thus usually have a lot of sales, etc. information for you. For example, for my Garbi, William Larkin Moore & Co. in Scottsdale, AZ is the sole US importer.
Good luck,
Mark