You may be thinking of the ACSI card available from Vicarious Books with a book of sites & maps, this is only of use in the off-peak season, which means not during August & maybe the last week in July.
I have an ACSI card but hardly use it & will not bother to subscribe again, only having it as an
insurance policy in case of not finding anywhere to stay, but this doesn't happen in Europe, with plenty of aires, wilding spots, harbour quays & beaches etc.
On a recent 8 week tour I stayed only 2 nights at a campsite & this was only because the camp at Santa Pola has a fantastic Van Wash, I used my ACSI card but only saved 2 euros.
I will not subscribe to the C.C. or C.& C.C. mafia, I'm of the age to have endured National Service & most english campsites remind me of army barracks with their rules & regulations, regimented rows etc.
Also, the people you meet wild camping or on aires seem more genuine & much friendlier than campsite types, many times we have been invited into larger vans for drinks etc., we have been given clams, mussels, fish & fruit & recently pulling in to the aire at Barre-de-Monts, we found it was full up, we were about to drive off, but two Frenchmen called us back & moved their vans to give us enough space. Can you imagine this happening in the UK?
Anyway whatever you do, enjoy your trip.
Best wishes,
spigot