I found this Etsy shop that has some acetate graph sheets for sale: https://www.etsy.com/uk/listing/125627579/acetate-graph-or-drafting... I'm not sure if she ships to Spain but you could ask her, or you could ask what brand those sheets are so that you can look for them in a European-based online store.
Hope this helps!
Thank you Thaneeya, I'll follow up on this.
Hi Thaneeya, Thanks again for the tip. I was able to get them from Esty. Now I just have to figure out how to use them.LOL