Need oscillating servo/stepper motor guidance
Unless you go with something big like a 1/2hp motor, you're going to have to build this yourself. The bearings on a small servo or stepper won't support that kind of load. You have to deal with the vertical thrust load of 30 lbs and then any torque caused by the load - motor axis not being perfectly vertical! You will need to build a base and a vertical support with bearings to carry the shaft. A couple of 2x4's would do it just fine. Or you could start with a floor lamp and toss the lamp head part.

Having said that, once the load is properly supported, it shouldn't be too hard to turn so a size 23 stepper motor will probably do it just fine.

How thick is the axis you want to turn? Maybe I can offer some suggestions on where to get the parts you need.