The Iberians don't 'do' Municipals like the french but thanks to those wonderful members of the Caravan Club who supply, free gratis and for nothing their thoughts on sites that they have visited in Spain, you can buy a book from the CC that has umpteen sites therein. Not all of the reviews are 'glowing' and as a result, you can sort the wheat from the chaff.
------------- How come when some people visit the fountain of knowledge, they only gargle!!!
ACSI sites are well represented in Spain, you could check out some of the reviews to give you a starting point perhaps. Otherwise, the Campingo website has a good selection of Spanish sites.
Don't forget to leave a review of the French and other European campsites you have visited!
Actually there are campings municipales in Spain, for instance,the one in Hospital de Orbigo in Leon is a municipal site.. not that I recommend it in the summer months. That said, municipal sites are few and far between and there doesn't seem to be a website with a list of municipal campsites in Spain.
I live on the north coast of Spain, so if you think I can help in any way, give me a shout.