Steam Oil is a lubricant specifically formulated to mix with steam as it enters the cylinder and lubricates the internal working parts of the engine in what can be very hostile conditions. It comes in a variety of grades with the heaviest being used in large high operating temperature engines down to the lightest grade as offered by MSM - International Grade 460.
Retail suppliers are rare and manufacturers have minimum order quantities that are too large for an imdividual to buy and use. The most readily available supplier will be a local steam club that is able to stock the larger quantity and fill smaller bottles for use by members and visitors.
We are not aware of any restrictions on posting the bottles we use - given we pay special attention to secure packaging.