If you only need one kitchen, I would avoid something like Citadines where you're giving up a lot to get a kitchen in every room. You just need to find hotels that have one special suite with kitchen facilities and for this you might need to contact hotels individually.

You should also think about what's needed in the kitchen. Is a microwave sufficient or do you need a stovetop with (how many?) burners? Do you need an oven? Full size refrigerator or is a smaller one, even (empty) minibar sized, sufficient? Do you need a freezer and if so, how large? Dishwasher? What about cooking equipment, plates, and silverware?