Hi @Hugh,
Though the correct canister depends on which type of Optimus backpacking stove you have, most are compatible with Isobutane-Propane fuel canisters like MSR IsoPro or Jetboil Jetpower.
Due to flammable shipping restrictions, we are not able to sell fuel canisters online, even while our retail locations are closed. Depending on where you live, you may be able to purchase canisters at hunting stores, or at Wal-Mart. MSR's website features a Dealer Locator to help you find retail locations that sell their fuel; however, you'll need to contact these locations to find out about their hours.
Hope this helps! Happy camping!
At REI, we believe time outside is fundamental to a life well lived.
