Hobby stores that carry r/c cars have silicone oil used as a shock damping oil. You can also find silicone oil at sewing machine shops, but I don't know what viscosity they carry.
Try to get the lowest weight oil you can. In the RC car world, that's probably 5wt or 10wt oil.
Oil I provide under the Airsoft Innovations label is 1.5wt.
Want nearly free GBB gas?