Office Supplies consists of all neccessory stuffs to run office or any organization like Office furniture, printing, technology equipment, breakroom supplies, cleaning products, health supplies etc. In case of stationery, it consists of printing papers, office files, teaching & learning materials, binders etc thus office stationery is subset of office supplies. But if you what to purchase stationery, office stationery term sounds more specific.
materials for writing and for using in an office, for example paper, pens and envelopes
special paper for writing letters on