Hi jvlobo.
Im from Spain too and im searchin a two way mirror too.
I ordered a film at amazon.
https://www.amazon.es/gp/product/B00280ENZ8ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1
I put them on a windowpane but the effect is terrible.
This week I will try to find a glass shop here in Murcia.
If I find something I will report here.