I found this 8-pack of Paper Mate triangular mechanical pencil set on Amazon. It's on sale for $2.97 (usually $6.29), and if you're subscribed to five items or more, you'll get an extra 10% off; pay just $2.67.
These pencils have a triangular shape because they're made to help kids develop early writing skills.
Take a look at more stationery deals and read about how Amazon Subscribe & Save works to help you save money on all your shopping.