Check the RC car sites. Quite a few viscosities of silicone oil out there, used in shocks on those things. My box has 10000, 50000, 100000, and 300000 viscosities that are all oils so you can get something that works well for most any application.
I spoke with someone at the company that makes the Air Venturi recommended oil. I was surprised to learn that Lowe's Kobalt oil comes fro the Same vat. At 1/3 the price and no shipping.