I don't have the answer regarding Spain - I would assume the answer is probably yes - but I don't know if there are extra requirements to obtain them.
But to the plane question... yes, you can bring medical supplies including syringes on the plane when you are also carrying the injectable medication. You do have to declare it when going through security checkpoints. I recommend you carry a copy of a prescription/medication pharmacy label so there is no confusion. They also recommend, but do not require, that medications be labelled (pharmacy label is sufficient. I often remove medications from their boxes - and I either cut out the medication label and bring it with - or ask for an extra label from the pharmacy and put it on the zip lock or other container that I keep medication in. Again - helps avoid confusion. I keep anything that I have to "declare" at the security checkpoint in a clear ziplock bag so I can easily remove it from the bag for inspection and the security folks can see what is in the bag without opening it up.