I'm a fan of the sister-run RockScissorPaper. They used to sell several scooter-themed stationery items, but I think the last of the line is their personalized stationery. I own two boxes and use them for special correspondence with folks who would appreciate the cool retro style and the cute Vespa.
For a limited time you can get this stationery (and many other themes) for 20% off. Follow this link to see all of the possible sets. But do it quickly as this sales only lasts through Thursday!