In the US, we tend to think of stationery as decorative writing paper with matching envelopes, or business letterhead with corresponding envelopes.
Pens, pencils, staplers, paper clips, file folders, etc., are usually referred to as "office supplies."
If you're referring to pens, pencils, erasers (what Americans call "rubbers"), rulers, three-ring binders, and things that students use at school, then we collectively call them "school supplies."
Back in the 1950s, early 1960s, it was common to buy such items at a "stationery store," but that phrase is somewhat archaic today. We buy office supplies at an office supply store (there are several "big box" chains, such as Office Max,
Office Depot, and Staples). These same stores also sell school supplies, as do department stores such as Wal-Mart.