most of the larger supermarkets/hypermarkets in france have an 'english' section and marmite is usually one of the things you can buy there, along with branston pickle, heinz salad cream and beans, and marmalade.
sorry, can't help you with spain.
You can get it in Spain, but it costs a fortune. If you've got room pop a jar in your suitcase.. I've had nearly two weeks here without it as I was over my weight limit... and I've only worn a bikini and a pair of shorts all week!! always pack far too much!!!