I was reading tiny tips for your model A book and on page 106 it states that lubriplate #8 is the same viscosity as "the old time steam oil" know as 600w. I dont know how old the entry in the book is so I am not sure if you can still get it. just a thought. I did find this link
http://www.lubriplate.com/pdf/pds/4_...nd_No.%208.pdf