The gold blades are LEGO part #98135 (Propeller 1 Blade 16L w/Axle [Sword Blade]).
Input the part number on Bricklink and you will note 13 sets which use the pearl gold version--mostly Ninjago sets.
(And as BadLarry & jason76basin stated, most LEGO parts have a tiny part number inscribed which can be inputted into the Bricklink database for further information. And if you know that what you have is definitely a LEGO part but it doesn't have an inscribed part number,
then you can pore through the voluminous Bricklink catalog, which is divided into multiple categories, until you locate such.
Plus, you can buy any missing parts to complete a set directly from Bricklink members.)