Cream charger bulbs that are unused/unopened can last for years. Typically the used by or best by date is shown on the package but not individual bulbs.
Once the cream chargers has been added to a whipped cream dispenser with some cream it can generally last in the refrigerator or up to two weeks. Nitrous oxide in the cream chargers is an anti-bacterial so will help to keep the cream fresh. Nitrous oxide cream chargers can be purchased online on this site.