I know the origional post requested a hard plastic case, but...

http://www.staples.com/office/supplies/p16__239157_Business_Supplies_10051_true_SEARCH

Staples has the Caselogic compact harddrive cases on sale this week for $10. They normally go $15-20 depending on where you shop. They will hold the heatsheet and then some- Airballrad uses one to carry a Heatsheet, PSP and Pocket Medic along with a few other tiny toys IIRC.