Where can I find adult pampers for a small woman?

My elder is a very small woman who needs to wear full briefs for her incontinence. Unfortunately, the smallest size we can find is still to large for her tiny legs. They do not seal well around her legs and that defeats their purpose. She has become housebound mainly because of her embarrassment as nothing seems to give her complete security.
I was wondering if there are any recommendations other caregivers have found to resolve this problem. I've wondered what hospitals do for their small patients (young or old) who are too big for toddler sizes but not big enough for small adults. Any help would be much appreciated!