Seems to me I found the information on the CMP forums. If I remember correctly there is a difference between straight linseed oil and boiled linseed oil. I don't remember the finer points. I think boiled is cut with solvents.
I was able to get linseed oil at Michaels (craft store) in their art (oil painting) department.
Be careful with any rags that end up soak in oil as it can become a fire hazard and even spontaneously combust.