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 of this are rare and manufacturers have minimum order quantities that are too large for an individual 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 of oil we offer - given we pay due attention to secure packaging.
Non-use of the recommended steam oil can lead to accelerated and irreparable wearing of moving parts inside the engine.
Click to read a very good article about steam oil.