I assume you are referring to butane/propane gas. In many countries (but not the UK where class difference or exclusivity/elitism tradition means a sort of mafia-like system where "not ours" is spat out and you are sent on your way, usually with some sort of guff about "unsafe from others") you can take any bottle to the places where they fill the local ones and have yours filled for a straight weight based charge (again unlike UK where the rip-off mentality reigns supreme). Whether Spain is one of these I can't say but you simply ask around to find out where the local ones go for refill. You will then have to go there - it is worth filling before you have quite run out if you are within reach. Ironically, I understand that in many areas in the UK the same refill place does all different brands but they won't talk to or deal with you (protectionism of sorts). The bottles of all UK brands are likely to be made abroad, probably the same place as the ones you see abroad, Portugal used to be a major source.