Do they make automatic DPDT switches that will switch on a timer to swap ground electrodes continuously?

This is actually for a high voltage application as well. 30 kV at the voltage supply.

 

I think you need to elaborate a lot more on the application. You want a DPDT switch to reverse the polarity a 30KV source?

Ken

 

You can get a DPDT relay to do the reversing.

Getting a relay to work at those voltages is the trick.