That sounds like an exciting project! We have a drawer of dye plants in Richmond Grows Seed Lending Library. I must say that some of the plants can be quite weedy, such as madder. I've been afraid to plant woad since I was warned that one can take over. I imagine where someone lives can make a difference on how much they spread.
We have a sweet little stamp that we use on packets that are dye plants and the drawer also has the image. Years ago we did a couple of natural dyeing classes through the seed library with a local natural dyer. They were a big hit!
Check out the page on SeedLibraries.net about dye plants. There is a picture of our dye stamp on it and some other resources. If you or someone else, does more with dye plants, we'd love to build this page out. If you are able to grow some fiber plants, you may want to consider adding those to your offerings.
You might want to look on the Sister Seed Library list to see if there are any seed libraries near you. It's organized by country. I believe there are some in Spain. UK definitely has some seed libraries. If there is a seed library in particular that you are interested in connecting with but you can't reach them, let me know and I can reach out to them to connect you.