Don't know whereabouts you are, but this might help ....http://www.segundamano.es/anuncios-catalunya/Bombonas-de-butano.htm?ca=43_s

if the link doesn't work for you type inn ' bombonas de butano' in the search box and select Catalunya/tarragona from the province menu.

there are loads for sale but being winter the price has jumped. They are now around TEN Euros each and as little as THREE Euros each. Or you can buy from the English and pay a minimum of 15 and more likely 20 Euros. they are only 15-25 euros when the English are selling them I'm afraid to say!